diff --git a/pkg/_fe_analyzer_shared/lib/src/scanner/io.dart b/pkg/_fe_analyzer_shared/lib/src/scanner/io.dart
index 04f95e9..066fe88 100644
--- a/pkg/_fe_analyzer_shared/lib/src/scanner/io.dart
+++ b/pkg/_fe_analyzer_shared/lib/src/scanner/io.dart
@@ -4,8 +4,6 @@
 
 library _fe_analyzer_shared.scanner.io;
 
-import 'dart:async' show Future;
-
 import 'dart:io' show File, RandomAccessFile;
 
 import 'dart:typed_data' show Uint8List;
diff --git a/pkg/analysis_server/benchmark/benchmarks.dart b/pkg/analysis_server/benchmark/benchmarks.dart
index f43c4e6..20ad9aa 100644
--- a/pkg/analysis_server/benchmark/benchmarks.dart
+++ b/pkg/analysis_server/benchmark/benchmarks.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 import 'dart:math' as math;
diff --git a/pkg/analysis_server/benchmark/perf/flutter_analyze_benchmark.dart b/pkg/analysis_server/benchmark/perf/flutter_analyze_benchmark.dart
index ede7ff8..e0008e8 100644
--- a/pkg/analysis_server/benchmark/perf/flutter_analyze_benchmark.dart
+++ b/pkg/analysis_server/benchmark/perf/flutter_analyze_benchmark.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
diff --git a/pkg/analysis_server/lib/plugin/edit/fix/fix_core.dart b/pkg/analysis_server/lib/plugin/edit/fix/fix_core.dart
index ea2d4ee..f63d1bd 100644
--- a/pkg/analysis_server/lib/plugin/edit/fix/fix_core.dart
+++ b/pkg/analysis_server/lib/plugin/edit/fix/fix_core.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/error/error.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart'
     show SourceChange;
diff --git a/pkg/analysis_server/lib/src/analysis_server_abstract.dart b/pkg/analysis_server/lib/src/analysis_server_abstract.dart
index 11d3066..c56feb0 100644
--- a/pkg/analysis_server/lib/src/analysis_server_abstract.dart
+++ b/pkg/analysis_server/lib/src/analysis_server_abstract.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:core';
 import 'dart:io' as io;
 
diff --git a/pkg/analysis_server/lib/src/channel/channel.dart b/pkg/analysis_server/lib/src/channel/channel.dart
index 6ee5072..f8807d2 100644
--- a/pkg/analysis_server/lib/src/channel/channel.dart
+++ b/pkg/analysis_server/lib/src/channel/channel.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:convert';
 
 import 'package:analysis_server/protocol/protocol.dart';
diff --git a/pkg/analysis_server/lib/src/cider/completion.dart b/pkg/analysis_server/lib/src/cider/completion.dart
index fac8c25..26e9582 100644
--- a/pkg/analysis_server/lib/src/cider/completion.dart
+++ b/pkg/analysis_server/lib/src/cider/completion.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/protocol_server.dart';
 import 'package:analysis_server/src/services/completion/completion_core.dart';
 import 'package:analysis_server/src/services/completion/completion_performance.dart';
diff --git a/pkg/analysis_server/lib/src/cider/fixes.dart b/pkg/analysis_server/lib/src/cider/fixes.dart
index 4944642..099287a 100644
--- a/pkg/analysis_server/lib/src/cider/fixes.dart
+++ b/pkg/analysis_server/lib/src/cider/fixes.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/plugin/edit/fix/fix_core.dart';
 import 'package:analysis_server/src/services/correction/change_workspace.dart';
 import 'package:analysis_server/src/services/correction/fix.dart';
diff --git a/pkg/analysis_server/lib/src/computer/import_elements_computer.dart b/pkg/analysis_server/lib/src/computer/import_elements_computer.dart
index d85e724..8dc38a7 100644
--- a/pkg/analysis_server/lib/src/computer/import_elements_computer.dart
+++ b/pkg/analysis_server/lib/src/computer/import_elements_computer.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analyzer/dart/analysis/results.dart';
 import 'package:analyzer/dart/ast/ast.dart';
diff --git a/pkg/analysis_server/lib/src/domain_analysis.dart b/pkg/analysis_server/lib/src/domain_analysis.dart
index b237a10..35f6911 100644
--- a/pkg/analysis_server/lib/src/domain_analysis.dart
+++ b/pkg/analysis_server/lib/src/domain_analysis.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:core';
 
 import 'package:analysis_server/protocol/protocol_constants.dart';
diff --git a/pkg/analysis_server/lib/src/domain_diagnostic.dart b/pkg/analysis_server/lib/src/domain_diagnostic.dart
index f095fba..58a03a6 100644
--- a/pkg/analysis_server/lib/src/domain_diagnostic.dart
+++ b/pkg/analysis_server/lib/src/domain_diagnostic.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:core';
 
 import 'package:analysis_server/protocol/protocol.dart';
diff --git a/pkg/analysis_server/lib/src/domain_kythe.dart b/pkg/analysis_server/lib/src/domain_kythe.dart
index 2937a4d..565c6cd 100644
--- a/pkg/analysis_server/lib/src/domain_kythe.dart
+++ b/pkg/analysis_server/lib/src/domain_kythe.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:core';
 
 import 'package:analysis_server/protocol/protocol.dart';
diff --git a/pkg/analysis_server/lib/src/domain_server.dart b/pkg/analysis_server/lib/src/domain_server.dart
index 628b9c2..c0d4e69 100644
--- a/pkg/analysis_server/lib/src/domain_server.dart
+++ b/pkg/analysis_server/lib/src/domain_server.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol.dart';
 import 'package:analysis_server/protocol/protocol_constants.dart';
 import 'package:analysis_server/protocol/protocol_generated.dart';
diff --git a/pkg/analysis_server/lib/src/domains/execution/completion.dart b/pkg/analysis_server/lib/src/domains/execution/completion.dart
index ff2796b..454be82 100644
--- a/pkg/analysis_server/lib/src/domains/execution/completion.dart
+++ b/pkg/analysis_server/lib/src/domains/execution/completion.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/protocol_server.dart'
     show
         CompletionSuggestion,
diff --git a/pkg/analysis_server/lib/src/lsp/handlers/commands/organize_imports.dart b/pkg/analysis_server/lib/src/lsp/handlers/commands/organize_imports.dart
index b7e4b62..85f8c67 100644
--- a/pkg/analysis_server/lib/src/lsp/handlers/commands/organize_imports.dart
+++ b/pkg/analysis_server/lib/src/lsp/handlers/commands/organize_imports.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/lsp_protocol/protocol_generated.dart';
 import 'package:analysis_server/lsp_protocol/protocol_special.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
diff --git a/pkg/analysis_server/lib/src/lsp/handlers/commands/perform_refactor.dart b/pkg/analysis_server/lib/src/lsp/handlers/commands/perform_refactor.dart
index ec0df60..c81db2e 100644
--- a/pkg/analysis_server/lib/src/lsp/handlers/commands/perform_refactor.dart
+++ b/pkg/analysis_server/lib/src/lsp/handlers/commands/perform_refactor.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/lsp_protocol/protocol_generated.dart';
 import 'package:analysis_server/lsp_protocol/protocol_special.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
diff --git a/pkg/analysis_server/lib/src/lsp/handlers/commands/send_workspace_edit.dart b/pkg/analysis_server/lib/src/lsp/handlers/commands/send_workspace_edit.dart
index 9cdb105..c918eb6 100644
--- a/pkg/analysis_server/lib/src/lsp/handlers/commands/send_workspace_edit.dart
+++ b/pkg/analysis_server/lib/src/lsp/handlers/commands/send_workspace_edit.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/lsp_protocol/protocol_generated.dart';
 import 'package:analysis_server/lsp_protocol/protocol_special.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
diff --git a/pkg/analysis_server/lib/src/lsp/handlers/commands/sort_members.dart b/pkg/analysis_server/lib/src/lsp/handlers/commands/sort_members.dart
index 06de050..c1a5b8f 100644
--- a/pkg/analysis_server/lib/src/lsp/handlers/commands/sort_members.dart
+++ b/pkg/analysis_server/lib/src/lsp/handlers/commands/sort_members.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/lsp_protocol/protocol_generated.dart';
 import 'package:analysis_server/lsp_protocol/protocol_special.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
diff --git a/pkg/analysis_server/lib/src/lsp/handlers/custom/handler_diagnostic_server.dart b/pkg/analysis_server/lib/src/lsp/handlers/custom/handler_diagnostic_server.dart
index facc544..9e3373a 100644
--- a/pkg/analysis_server/lib/src/lsp/handlers/custom/handler_diagnostic_server.dart
+++ b/pkg/analysis_server/lib/src/lsp/handlers/custom/handler_diagnostic_server.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/lsp_protocol/protocol_custom_generated.dart';
 import 'package:analysis_server/lsp_protocol/protocol_generated.dart';
 import 'package:analysis_server/lsp_protocol/protocol_special.dart';
diff --git a/pkg/analysis_server/lib/src/lsp/handlers/custom/handler_reanalyze.dart b/pkg/analysis_server/lib/src/lsp/handlers/custom/handler_reanalyze.dart
index ad5c1b3..68a04e9 100644
--- a/pkg/analysis_server/lib/src/lsp/handlers/custom/handler_reanalyze.dart
+++ b/pkg/analysis_server/lib/src/lsp/handlers/custom/handler_reanalyze.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/lsp_protocol/protocol_generated.dart';
 import 'package:analysis_server/lsp_protocol/protocol_special.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
diff --git a/pkg/analysis_server/lib/src/lsp/handlers/custom/handler_super.dart b/pkg/analysis_server/lib/src/lsp/handlers/custom/handler_super.dart
index 094fbdd..b33967f 100644
--- a/pkg/analysis_server/lib/src/lsp/handlers/custom/handler_super.dart
+++ b/pkg/analysis_server/lib/src/lsp/handlers/custom/handler_super.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/lsp_protocol/protocol_generated.dart';
 import 'package:analysis_server/lsp_protocol/protocol_special.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
diff --git a/pkg/analysis_server/lib/src/lsp/handlers/handler_code_actions.dart b/pkg/analysis_server/lib/src/lsp/handlers/handler_code_actions.dart
index 2358cee..6fb0452 100644
--- a/pkg/analysis_server/lib/src/lsp/handlers/handler_code_actions.dart
+++ b/pkg/analysis_server/lib/src/lsp/handlers/handler_code_actions.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:collection';
 
 import 'package:analysis_server/lsp_protocol/protocol_generated.dart';
diff --git a/pkg/analysis_server/lib/src/lsp/handlers/handler_completion.dart b/pkg/analysis_server/lib/src/lsp/handlers/handler_completion.dart
index 272057f..8d75c98 100644
--- a/pkg/analysis_server/lib/src/lsp/handlers/handler_completion.dart
+++ b/pkg/analysis_server/lib/src/lsp/handlers/handler_completion.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:collection';
 
 import 'package:analysis_server/lsp_protocol/protocol_generated.dart';
diff --git a/pkg/analysis_server/lib/src/lsp/handlers/handler_completion_resolve.dart b/pkg/analysis_server/lib/src/lsp/handlers/handler_completion_resolve.dart
index 63ce7d0..d7f1610 100644
--- a/pkg/analysis_server/lib/src/lsp/handlers/handler_completion_resolve.dart
+++ b/pkg/analysis_server/lib/src/lsp/handlers/handler_completion_resolve.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/lsp_protocol/protocol_generated.dart';
 import 'package:analysis_server/lsp_protocol/protocol_special.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
diff --git a/pkg/analysis_server/lib/src/lsp/handlers/handler_definition.dart b/pkg/analysis_server/lib/src/lsp/handlers/handler_definition.dart
index b378a96..43bf70c 100644
--- a/pkg/analysis_server/lib/src/lsp/handlers/handler_definition.dart
+++ b/pkg/analysis_server/lib/src/lsp/handlers/handler_definition.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/lsp_protocol/protocol_generated.dart';
 import 'package:analysis_server/lsp_protocol/protocol_special.dart';
 import 'package:analysis_server/protocol/protocol_generated.dart'
diff --git a/pkg/analysis_server/lib/src/lsp/handlers/handler_document_highlights.dart b/pkg/analysis_server/lib/src/lsp/handlers/handler_document_highlights.dart
index 81a1fdd..8044281 100644
--- a/pkg/analysis_server/lib/src/lsp/handlers/handler_document_highlights.dart
+++ b/pkg/analysis_server/lib/src/lsp/handlers/handler_document_highlights.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/lsp_protocol/protocol_generated.dart';
 import 'package:analysis_server/lsp_protocol/protocol_special.dart';
 import 'package:analysis_server/src/domains/analysis/occurrences.dart';
diff --git a/pkg/analysis_server/lib/src/lsp/handlers/handler_document_symbols.dart b/pkg/analysis_server/lib/src/lsp/handlers/handler_document_symbols.dart
index eaba645..2e383a0 100644
--- a/pkg/analysis_server/lib/src/lsp/handlers/handler_document_symbols.dart
+++ b/pkg/analysis_server/lib/src/lsp/handlers/handler_document_symbols.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:collection';
 
 import 'package:analysis_server/lsp_protocol/protocol_generated.dart';
diff --git a/pkg/analysis_server/lib/src/lsp/handlers/handler_execute_command.dart b/pkg/analysis_server/lib/src/lsp/handlers/handler_execute_command.dart
index cbfba5c..22b99d1 100644
--- a/pkg/analysis_server/lib/src/lsp/handlers/handler_execute_command.dart
+++ b/pkg/analysis_server/lib/src/lsp/handlers/handler_execute_command.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/lsp_protocol/protocol_generated.dart';
 import 'package:analysis_server/lsp_protocol/protocol_special.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
diff --git a/pkg/analysis_server/lib/src/lsp/handlers/handler_exit.dart b/pkg/analysis_server/lib/src/lsp/handlers/handler_exit.dart
index 8ac5d58..82b3f07 100644
--- a/pkg/analysis_server/lib/src/lsp/handlers/handler_exit.dart
+++ b/pkg/analysis_server/lib/src/lsp/handlers/handler_exit.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:io';
 
 import 'package:analysis_server/lsp_protocol/protocol_generated.dart';
diff --git a/pkg/analysis_server/lib/src/lsp/handlers/handler_folding.dart b/pkg/analysis_server/lib/src/lsp/handlers/handler_folding.dart
index 418e84d..988b719 100644
--- a/pkg/analysis_server/lib/src/lsp/handlers/handler_folding.dart
+++ b/pkg/analysis_server/lib/src/lsp/handlers/handler_folding.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/lsp_protocol/protocol_generated.dart';
 import 'package:analysis_server/lsp_protocol/protocol_special.dart';
 import 'package:analysis_server/src/computer/computer_folding.dart';
diff --git a/pkg/analysis_server/lib/src/lsp/handlers/handler_format_on_type.dart b/pkg/analysis_server/lib/src/lsp/handlers/handler_format_on_type.dart
index 22e60af..ad0869e 100644
--- a/pkg/analysis_server/lib/src/lsp/handlers/handler_format_on_type.dart
+++ b/pkg/analysis_server/lib/src/lsp/handlers/handler_format_on_type.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/lsp_protocol/protocol_generated.dart';
 import 'package:analysis_server/lsp_protocol/protocol_special.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
diff --git a/pkg/analysis_server/lib/src/lsp/handlers/handler_formatting.dart b/pkg/analysis_server/lib/src/lsp/handlers/handler_formatting.dart
index 2ca27ef..031d5a9 100644
--- a/pkg/analysis_server/lib/src/lsp/handlers/handler_formatting.dart
+++ b/pkg/analysis_server/lib/src/lsp/handlers/handler_formatting.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/lsp_protocol/protocol_generated.dart';
 import 'package:analysis_server/lsp_protocol/protocol_special.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
diff --git a/pkg/analysis_server/lib/src/lsp/handlers/handler_hover.dart b/pkg/analysis_server/lib/src/lsp/handlers/handler_hover.dart
index 72bc4d6..3b5561e 100644
--- a/pkg/analysis_server/lib/src/lsp/handlers/handler_hover.dart
+++ b/pkg/analysis_server/lib/src/lsp/handlers/handler_hover.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/lsp_protocol/protocol_generated.dart';
 import 'package:analysis_server/lsp_protocol/protocol_special.dart';
 import 'package:analysis_server/protocol/protocol_generated.dart';
diff --git a/pkg/analysis_server/lib/src/lsp/handlers/handler_implementation.dart b/pkg/analysis_server/lib/src/lsp/handlers/handler_implementation.dart
index ee143e7..17a3b28 100644
--- a/pkg/analysis_server/lib/src/lsp/handlers/handler_implementation.dart
+++ b/pkg/analysis_server/lib/src/lsp/handlers/handler_implementation.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/lsp_protocol/protocol_generated.dart';
 import 'package:analysis_server/lsp_protocol/protocol_special.dart';
 import 'package:analysis_server/protocol/protocol_generated.dart';
diff --git a/pkg/analysis_server/lib/src/lsp/handlers/handler_initialized.dart b/pkg/analysis_server/lib/src/lsp/handlers/handler_initialized.dart
index f8d0c66..b42d11f 100644
--- a/pkg/analysis_server/lib/src/lsp/handlers/handler_initialized.dart
+++ b/pkg/analysis_server/lib/src/lsp/handlers/handler_initialized.dart
@@ -31,7 +31,7 @@
     await server.fetchClientConfigurationAndPerformDynamicRegistration();
 
     if (!server.initializationOptions.onlyAnalyzeProjectsWithOpenFiles) {
-      server.setAnalysisRoots(openWorkspacePaths);
+      server.updateAnalysisRoots(openWorkspacePaths, const []);
     }
 
     return success();
diff --git a/pkg/analysis_server/lib/src/lsp/handlers/handler_references.dart b/pkg/analysis_server/lib/src/lsp/handlers/handler_references.dart
index bf4094e..4dc81df 100644
--- a/pkg/analysis_server/lib/src/lsp/handlers/handler_references.dart
+++ b/pkg/analysis_server/lib/src/lsp/handlers/handler_references.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/lsp_protocol/protocol_generated.dart';
 import 'package:analysis_server/lsp_protocol/protocol_special.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
diff --git a/pkg/analysis_server/lib/src/lsp/handlers/handler_signature_help.dart b/pkg/analysis_server/lib/src/lsp/handlers/handler_signature_help.dart
index 0d4623b..9627589 100644
--- a/pkg/analysis_server/lib/src/lsp/handlers/handler_signature_help.dart
+++ b/pkg/analysis_server/lib/src/lsp/handlers/handler_signature_help.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/lsp_protocol/protocol_generated.dart';
 import 'package:analysis_server/lsp_protocol/protocol_special.dart';
 import 'package:analysis_server/src/computer/computer_signature.dart';
diff --git a/pkg/analysis_server/lib/src/lsp/handlers/handler_states.dart b/pkg/analysis_server/lib/src/lsp/handlers/handler_states.dart
index acecc86..949777a 100644
--- a/pkg/analysis_server/lib/src/lsp/handlers/handler_states.dart
+++ b/pkg/analysis_server/lib/src/lsp/handlers/handler_states.dart
@@ -62,17 +62,11 @@
     registerHandler(ShutdownMessageHandler(server));
     registerHandler(ExitMessageHandler(server));
     registerHandler(
-      TextDocumentOpenHandler(
-        server,
-        server.initializationOptions.onlyAnalyzeProjectsWithOpenFiles,
-      ),
+      TextDocumentOpenHandler(server),
     );
     registerHandler(TextDocumentChangeHandler(server));
     registerHandler(
-      TextDocumentCloseHandler(
-        server,
-        server.initializationOptions.onlyAnalyzeProjectsWithOpenFiles,
-      ),
+      TextDocumentCloseHandler(server),
     );
     registerHandler(HoverHandler(server));
     registerHandler(CompletionHandler(
diff --git a/pkg/analysis_server/lib/src/lsp/handlers/handler_text_document_changes.dart b/pkg/analysis_server/lib/src/lsp/handlers/handler_text_document_changes.dart
index 6a4b026..6e6309a 100644
--- a/pkg/analysis_server/lib/src/lsp/handlers/handler_text_document_changes.dart
+++ b/pkg/analysis_server/lib/src/lsp/handlers/handler_text_document_changes.dart
@@ -77,11 +77,7 @@
 
 class TextDocumentCloseHandler
     extends MessageHandler<DidCloseTextDocumentParams, void> {
-  /// Whether analysis roots are based on open files and should be updated.
-  bool updateAnalysisRoots;
-
-  TextDocumentCloseHandler(LspAnalysisServer server, this.updateAnalysisRoots)
-      : super(server);
+  TextDocumentCloseHandler(LspAnalysisServer server) : super(server);
 
   @override
   Method get handlesMessage => Method.textDocument_didClose;
@@ -98,25 +94,7 @@
       server.removePriorityFile(path);
       server.documentVersions.remove(path);
       server.onOverlayDestroyed(path);
-
-      if (updateAnalysisRoots) {
-        // If there are no other open files in this context, we can remove it
-        // from the analysis roots.
-        final contextFolder = server.contextManager.getContextFolderFor(path);
-        var hasOtherFilesInContext = false;
-        for (var otherDocPath in server.documentVersions.keys) {
-          if (server.contextManager.getContextFolderFor(otherDocPath) ==
-              contextFolder) {
-            hasOtherFilesInContext = true;
-            break;
-          }
-        }
-        if (!hasOtherFilesInContext) {
-          final projectFolder =
-              _findProjectFolder(server.resourceProvider, path);
-          server.updateAnalysisRoots([], [projectFolder]);
-        }
-      }
+      server.removeTemporaryAnalysisRoot(path);
 
       return success();
     });
@@ -125,13 +103,7 @@
 
 class TextDocumentOpenHandler
     extends MessageHandler<DidOpenTextDocumentParams, void> {
-  /// Whether analysis roots are based on open files and should be updated.
-  bool updateAnalysisRoots;
-
-  DateTime lastSentAnalyzeOpenFilesWarnings;
-
-  TextDocumentOpenHandler(LspAnalysisServer server, this.updateAnalysisRoots)
-      : super(server);
+  TextDocumentOpenHandler(LspAnalysisServer server) : super(server);
 
   @override
   Method get handlesMessage => Method.textDocument_didOpen;
@@ -160,32 +132,15 @@
 
       driver?.addFile(path);
 
-      // If there was no current driver for this file, then we may need to add
-      // its project folder as an analysis root.
-      if (updateAnalysisRoots && driver == null) {
-        final projectFolder = _findProjectFolder(server.resourceProvider, path);
-        if (projectFolder != null) {
-          server.updateAnalysisRoots([projectFolder], []);
-        } else {
-          // There was no pubspec - ideally we should add just the file
-          // here but we don't currently support that.
-          // https://github.com/dart-lang/sdk/issues/32256
-
-          // Send a warning to the user, but only if we haven't already in the
-          // last 60 seconds.
-          if (lastSentAnalyzeOpenFilesWarnings == null ||
-              (DateTime.now()
-                      .difference(lastSentAnalyzeOpenFilesWarnings)
-                      .inSeconds >
-                  60)) {
-            lastSentAnalyzeOpenFilesWarnings = DateTime.now();
-            server.showMessageToUser(
-                MessageType.Warning,
-                'When using onlyAnalyzeProjectsWithOpenFiles, files opened that '
-                'are not contained within project folders containing pubspec.yaml, '
-                '.packages or BUILD files will not be analyzed.');
-          }
-        }
+      // Figure out the best analysis root for this file and register it as a temporary
+      // analysis root. We need to register it even if we found a driver, so that if
+      // the driver existed only because of another open file, it will not be removed
+      // when that file is closed.
+      final analysisRoot = driver?.contextRoot?.root ??
+          _findProjectFolder(server.resourceProvider, path) ??
+          dirname(path);
+      if (analysisRoot != null) {
+        server.addTemporaryAnalysisRoot(path, analysisRoot);
       }
 
       server.addPriorityFile(path);
diff --git a/pkg/analysis_server/lib/src/lsp/handlers/handler_workspace_symbols.dart b/pkg/analysis_server/lib/src/lsp/handlers/handler_workspace_symbols.dart
index c1cce0a..fece08b 100644
--- a/pkg/analysis_server/lib/src/lsp/handlers/handler_workspace_symbols.dart
+++ b/pkg/analysis_server/lib/src/lsp/handlers/handler_workspace_symbols.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:collection';
 
 import 'package:analysis_server/lsp_protocol/protocol_generated.dart';
diff --git a/pkg/analysis_server/lib/src/lsp/lsp_analysis_server.dart b/pkg/analysis_server/lib/src/lsp/lsp_analysis_server.dart
index e5dd73c..027f52e 100644
--- a/pkg/analysis_server/lib/src/lsp/lsp_analysis_server.dart
+++ b/pkg/analysis_server/lib/src/lsp/lsp_analysis_server.dart
@@ -102,6 +102,21 @@
 
   StreamSubscription _pluginChangeSubscription;
 
+  /// Temporary analysis roots for open files.
+  ///
+  /// When a file is opened and there is no driver available (for example no
+  /// folder was opened in the editor, so the set of analysis roots is empty)
+  /// we add temporary roots for the project (or containing) folder. When the
+  /// file is closed, it is removed from this map and if no other open file
+  /// uses that root, it will be removed from the set of analysis roots.
+  ///
+  /// key: file path of the open file
+  /// value: folder to be used as a root.
+  final _temporaryAnalysisRoots = <String, String>{};
+
+  /// The set of analysis roots explicitly added to the workspace.
+  final _explicitAnalysisRoots = HashSet<String>();
+
   /// Initialize a newly created server to send and receive messages to the
   /// given [channel].
   LspAnalysisServer(
@@ -170,6 +185,12 @@
     }
   }
 
+  /// Adds a temporary analysis root for an open file.
+  void addTemporaryAnalysisRoot(String filePath, String folderPath) {
+    _temporaryAnalysisRoots[filePath] = folderPath;
+    _refreshAnalysisRoots();
+  }
+
   /// The socket from which messages are being read has been closed.
   void done() {}
 
@@ -417,6 +438,12 @@
     }
   }
 
+  /// Removes any temporary analysis root for a file that was closed.
+  void removeTemporaryAnalysisRoot(String filePath) {
+    _temporaryAnalysisRoots.remove(filePath);
+    _refreshAnalysisRoots();
+  }
+
   void sendErrorResponse(Message message, ResponseError error) {
     if (message is RequestMessage) {
       channel.sendResponse(ResponseMessage(
@@ -492,14 +519,6 @@
     ));
   }
 
-  void setAnalysisRoots(List<String> includedPaths) {
-    declarationsTracker?.discardContexts();
-    final uniquePaths = HashSet<String>.of(includedPaths ?? const []);
-    notificationManager.setAnalysisRoots(includedPaths, []);
-    contextManager.setRoots(uniquePaths.toList(), []);
-    addContextsToDeclarationsTracker();
-  }
-
   /// Returns `true` if closing labels should be sent for [file] with the given
   /// absolute path.
   bool shouldSendClosingLabelsFor(String file) {
@@ -567,12 +586,12 @@
 
   void updateAnalysisRoots(List<String> addedPaths, List<String> removedPaths) {
     // TODO(dantup): This is currently case-sensitive!
-    final newPaths =
-        HashSet<String>.of(contextManager.includedPaths ?? const [])
-          ..addAll(addedPaths ?? const [])
-          ..removeAll(removedPaths ?? const []);
 
-    setAnalysisRoots(newPaths.toList());
+    _explicitAnalysisRoots
+      ..addAll(addedPaths ?? const [])
+      ..removeAll(removedPaths ?? const []);
+
+    _refreshAnalysisRoots();
   }
 
   void _afterOverlayChanged(String path, dynamic changeForPlugins) {
@@ -589,6 +608,18 @@
     capabilitiesComputer.performDynamicRegistration();
   }
 
+  void _refreshAnalysisRoots() {
+    // Always include any temporary analysis roots for open files.
+    final includedPaths = HashSet<String>.of(_explicitAnalysisRoots)
+      ..addAll(_temporaryAnalysisRoots.values)
+      ..toList();
+
+    declarationsTracker?.discardContexts();
+    notificationManager.setAnalysisRoots(includedPaths.toList(), []);
+    contextManager.setRoots(includedPaths.toList(), []);
+    addContextsToDeclarationsTracker();
+  }
+
   void _updateDriversAndPluginsPriorityFiles() {
     final priorityFilesList = priorityFiles.toList();
     driverMap.values.forEach((driver) {
diff --git a/pkg/analysis_server/lib/src/operation/operation_analysis.dart b/pkg/analysis_server/lib/src/operation/operation_analysis.dart
index feb124f..c26fd4a 100644
--- a/pkg/analysis_server/lib/src/operation/operation_analysis.dart
+++ b/pkg/analysis_server/lib/src/operation/operation_analysis.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/computer/computer_closingLabels.dart';
 import 'package:analysis_server/src/computer/computer_folding.dart';
diff --git a/pkg/analysis_server/lib/src/provisional/completion/completion_core.dart b/pkg/analysis_server/lib/src/provisional/completion/completion_core.dart
index a15d108..06e7ddb 100644
--- a/pkg/analysis_server/lib/src/provisional/completion/completion_core.dart
+++ b/pkg/analysis_server/lib/src/provisional/completion/completion_core.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/dart/analysis/results.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/src/generated/source.dart';
diff --git a/pkg/analysis_server/lib/src/provisional/completion/dart/completion_dart.dart b/pkg/analysis_server/lib/src/provisional/completion/dart/completion_dart.dart
index be79ccd..6b1c732 100644
--- a/pkg/analysis_server/lib/src/provisional/completion/dart/completion_dart.dart
+++ b/pkg/analysis_server/lib/src/provisional/completion/dart/completion_dart.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/provisional/completion/completion_core.dart';
 import 'package:analysis_server/src/services/completion/dart/feature_computer.dart';
 import 'package:analysis_server/src/services/completion/dart/suggestion_builder.dart';
diff --git a/pkg/analysis_server/lib/src/search/element_references.dart b/pkg/analysis_server/lib/src/search/element_references.dart
index ba332d9..dc07265 100644
--- a/pkg/analysis_server/lib/src/search/element_references.dart
+++ b/pkg/analysis_server/lib/src/search/element_references.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/protocol_server.dart'
     show SearchResult, newSearchResult_fromMatch;
 import 'package:analysis_server/src/services/search/hierarchy.dart';
diff --git a/pkg/analysis_server/lib/src/search/search_domain.dart b/pkg/analysis_server/lib/src/search/search_domain.dart
index e3ad323..93b2db4 100644
--- a/pkg/analysis_server/lib/src/search/search_domain.dart
+++ b/pkg/analysis_server/lib/src/search/search_domain.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol_constants.dart';
 import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/protocol_server.dart' as protocol;
diff --git a/pkg/analysis_server/lib/src/search/type_hierarchy.dart b/pkg/analysis_server/lib/src/search/type_hierarchy.dart
index 91c2a9b..d5b1804 100644
--- a/pkg/analysis_server/lib/src/search/type_hierarchy.dart
+++ b/pkg/analysis_server/lib/src/search/type_hierarchy.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:collection';
 
 import 'package:analysis_server/src/protocol_server.dart'
diff --git a/pkg/analysis_server/lib/src/server/diagnostic_server.dart b/pkg/analysis_server/lib/src/server/diagnostic_server.dart
index 42fa9b9..4a0a27a0 100644
--- a/pkg/analysis_server/lib/src/server/diagnostic_server.dart
+++ b/pkg/analysis_server/lib/src/server/diagnostic_server.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 /// A handle to start, and return the current port of, a diagnostic server.
 abstract class DiagnosticServer {
   /// Return the port of the diagnostic web server. If the server is not running
diff --git a/pkg/analysis_server/lib/src/server/http_server.dart b/pkg/analysis_server/lib/src/server/http_server.dart
index 394cb9a..1083d5c 100644
--- a/pkg/analysis_server/lib/src/server/http_server.dart
+++ b/pkg/analysis_server/lib/src/server/http_server.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:io';
 
 import 'package:analysis_server/src/socket_server.dart';
diff --git a/pkg/analysis_server/lib/src/server/isolate_analysis_server.dart b/pkg/analysis_server/lib/src/server/isolate_analysis_server.dart
index 151bcdf..2ef30d3 100644
--- a/pkg/analysis_server/lib/src/server/isolate_analysis_server.dart
+++ b/pkg/analysis_server/lib/src/server/isolate_analysis_server.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:io' show IOSink;
 import 'dart:isolate';
 
diff --git a/pkg/analysis_server/lib/src/server/lsp_stdio_server.dart b/pkg/analysis_server/lib/src/server/lsp_stdio_server.dart
index d73ef3e..2fa5b8a 100644
--- a/pkg/analysis_server/lib/src/server/lsp_stdio_server.dart
+++ b/pkg/analysis_server/lib/src/server/lsp_stdio_server.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:io';
 
 import 'package:analysis_server/src/lsp/channel/lsp_byte_stream_channel.dart';
diff --git a/pkg/analysis_server/lib/src/server/stdio_server.dart b/pkg/analysis_server/lib/src/server/stdio_server.dart
index 322997d..06c5030 100644
--- a/pkg/analysis_server/lib/src/server/stdio_server.dart
+++ b/pkg/analysis_server/lib/src/server/stdio_server.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:io';
 
 import 'package:analysis_server/src/channel/byte_stream_channel.dart';
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/arglist_contributor.dart b/pkg/analysis_server/lib/src/services/completion/dart/arglist_contributor.dart
index cc88ab0..01b7721 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/arglist_contributor.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/arglist_contributor.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/completion/dart/suggestion_builder.dart';
 import 'package:analysis_server/src/utilities/flutter.dart';
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/combinator_contributor.dart b/pkg/analysis_server/lib/src/services/completion/dart/combinator_contributor.dart
index ab2768d..ebebb68 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/combinator_contributor.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/combinator_contributor.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/protocol_server.dart'
     hide Element, ElementKind;
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/common_usage_sorter.dart b/pkg/analysis_server/lib/src/services/completion/dart/common_usage_sorter.dart
index ca458ee..d553529 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/common_usage_sorter.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/common_usage_sorter.dart
@@ -4,8 +4,6 @@
 
 library services.completion.dart.sorter.common;
 
-import 'dart:async';
-
 import 'package:analysis_server/src/protocol_server.dart' as protocol;
 import 'package:analysis_server/src/protocol_server.dart'
     show CompletionSuggestion, CompletionSuggestionKind;
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/completion_manager.dart b/pkg/analysis_server/lib/src/services/completion/dart/completion_manager.dart
index 0f1267b..f6dc272 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/completion_manager.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/completion_manager.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/protocol_server.dart';
 import 'package:analysis_server/src/provisional/completion/completion_core.dart'
     show AbortCompletion, CompletionRequest;
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/completion_ranking.dart b/pkg/analysis_server/lib/src/services/completion/dart/completion_ranking.dart
index 6be6f54..021aaf8 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/completion_ranking.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/completion_ranking.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:collection';
 import 'dart:isolate';
 
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/contribution_sorter.dart b/pkg/analysis_server/lib/src/services/completion/dart/contribution_sorter.dart
index e9c9fb1..e2889ab 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/contribution_sorter.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/contribution_sorter.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
 
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/extension_member_contributor.dart b/pkg/analysis_server/lib/src/services/completion/dart/extension_member_contributor.dart
index c2b2573..6779aa9 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/extension_member_contributor.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/extension_member_contributor.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/completion/dart/suggestion_builder.dart';
 import 'package:analyzer/dart/ast/ast.dart';
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/field_formal_contributor.dart b/pkg/analysis_server/lib/src/services/completion/dart/field_formal_contributor.dart
index 4135698..a24d5c4 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/field_formal_contributor.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/field_formal_contributor.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/completion/dart/suggestion_builder.dart';
 import 'package:analyzer/dart/ast/ast.dart';
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/imported_reference_contributor.dart b/pkg/analysis_server/lib/src/services/completion/dart/imported_reference_contributor.dart
index b2c1335..4f560e3 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/imported_reference_contributor.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/imported_reference_contributor.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/completion/dart/local_library_contributor.dart';
 import 'package:analysis_server/src/services/completion/dart/suggestion_builder.dart'
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/keyword_contributor.dart b/pkg/analysis_server/lib/src/services/completion/dart/keyword_contributor.dart
index 443caa9..979b63f 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/keyword_contributor.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/keyword_contributor.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/completion/dart/completion_manager.dart';
 import 'package:analysis_server/src/services/completion/dart/suggestion_builder.dart';
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/label_contributor.dart b/pkg/analysis_server/lib/src/services/completion/dart/label_contributor.dart
index 463e66e..9434271 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/label_contributor.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/label_contributor.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/completion/dart/completion_manager.dart'
     show DartCompletionRequestImpl;
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/library_member_contributor.dart b/pkg/analysis_server/lib/src/services/completion/dart/library_member_contributor.dart
index d25bbb8..4801bf8 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/library_member_contributor.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/library_member_contributor.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/protocol_server.dart'
     show CompletionSuggestionKind;
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/library_prefix_contributor.dart b/pkg/analysis_server/lib/src/services/completion/dart/library_prefix_contributor.dart
index 019aba1..0fccab2 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/library_prefix_contributor.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/library_prefix_contributor.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/completion/dart/suggestion_builder.dart';
 
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/local_library_contributor.dart b/pkg/analysis_server/lib/src/services/completion/dart/local_library_contributor.dart
index ac04121..33d22cf 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/local_library_contributor.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/local_library_contributor.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/protocol_server.dart'
     show CompletionSuggestionKind;
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/local_reference_contributor.dart b/pkg/analysis_server/lib/src/services/completion/dart/local_reference_contributor.dart
index a9fbc91..9bbc308 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/local_reference_contributor.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/local_reference_contributor.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/protocol_server.dart'
     show CompletionSuggestionKind;
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/named_constructor_contributor.dart b/pkg/analysis_server/lib/src/services/completion/dart/named_constructor_contributor.dart
index 40e76cf..316d282 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/named_constructor_contributor.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/named_constructor_contributor.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/completion/dart/suggestion_builder.dart';
 import 'package:analyzer/dart/ast/ast.dart';
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/override_contributor.dart b/pkg/analysis_server/lib/src/services/completion/dart/override_contributor.dart
index de4912c..178dc1d 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/override_contributor.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/override_contributor.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/completion/dart/suggestion_builder.dart';
 import 'package:analyzer/dart/ast/ast.dart';
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/static_member_contributor.dart b/pkg/analysis_server/lib/src/services/completion/dart/static_member_contributor.dart
index 626db62..abe003d 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/static_member_contributor.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/static_member_contributor.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/completion/dart/suggestion_builder.dart';
 import 'package:analyzer/dart/ast/ast.dart';
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/type_member_contributor.dart b/pkg/analysis_server/lib/src/services/completion/dart/type_member_contributor.dart
index e416f0c..3120c99 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/type_member_contributor.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/type_member_contributor.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:collection';
 
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/uri_contributor.dart b/pkg/analysis_server/lib/src/services/completion/dart/uri_contributor.dart
index c27c960..b832581 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/uri_contributor.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/uri_contributor.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:core';
 
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/variable_name_contributor.dart b/pkg/analysis_server/lib/src/services/completion/dart/variable_name_contributor.dart
index c8955d0..1c4e0db 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/variable_name_contributor.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/variable_name_contributor.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/completion/dart/suggestion_builder.dart';
 import 'package:analysis_server/src/services/correction/name_suggestion.dart';
diff --git a/pkg/analysis_server/lib/src/services/completion/postfix/postfix_completion.dart b/pkg/analysis_server/lib/src/services/completion/postfix/postfix_completion.dart
index b743ff3..403fbb3 100644
--- a/pkg/analysis_server/lib/src/services/completion/postfix/postfix_completion.dart
+++ b/pkg/analysis_server/lib/src/services/completion/postfix/postfix_completion.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/protocol_server.dart' hide Element;
 import 'package:analysis_server/src/services/correction/util.dart';
 import 'package:analyzer/dart/analysis/results.dart';
diff --git a/pkg/analysis_server/lib/src/services/completion/statement/statement_completion.dart b/pkg/analysis_server/lib/src/services/completion/statement/statement_completion.dart
index 6c0dc57..808cb44 100644
--- a/pkg/analysis_server/lib/src/services/completion/statement/statement_completion.dart
+++ b/pkg/analysis_server/lib/src/services/completion/statement/statement_completion.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:math';
 
 import 'package:analysis_server/src/protocol_server.dart' hide Element;
diff --git a/pkg/analysis_server/lib/src/services/correction/assist_internal.dart b/pkg/analysis_server/lib/src/services/correction/assist_internal.dart
index 2f3c330..357c58f 100644
--- a/pkg/analysis_server/lib/src/services/correction/assist_internal.dart
+++ b/pkg/analysis_server/lib/src/services/correction/assist_internal.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/plugin/edit/assist/assist_core.dart';
 import 'package:analysis_server/plugin/edit/assist/assist_dart.dart';
 import 'package:analysis_server/src/services/correction/assist.dart';
diff --git a/pkg/analysis_server/lib/src/services/correction/bulk_fix_processor.dart b/pkg/analysis_server/lib/src/services/correction/bulk_fix_processor.dart
index e20987b..8ca0596 100644
--- a/pkg/analysis_server/lib/src/services/correction/bulk_fix_processor.dart
+++ b/pkg/analysis_server/lib/src/services/correction/bulk_fix_processor.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:core';
 
 import 'package:analysis_server/plugin/edit/fix/fix_dart.dart';
diff --git a/pkg/analysis_server/lib/src/services/correction/executable_parameters.dart b/pkg/analysis_server/lib/src/services/correction/executable_parameters.dart
index 6ced314..5c93ac9 100644
--- a/pkg/analysis_server/lib/src/services/correction/executable_parameters.dart
+++ b/pkg/analysis_server/lib/src/services/correction/executable_parameters.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:core';
 
 import 'package:analyzer/dart/ast/ast.dart';
diff --git a/pkg/analysis_server/lib/src/services/correction/fix_internal.dart b/pkg/analysis_server/lib/src/services/correction/fix_internal.dart
index 6d408cd..4740406 100644
--- a/pkg/analysis_server/lib/src/services/correction/fix_internal.dart
+++ b/pkg/analysis_server/lib/src/services/correction/fix_internal.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:core';
 
 import 'package:analysis_server/plugin/edit/fix/fix_core.dart';
diff --git a/pkg/analysis_server/lib/src/services/refactoring/convert_getter_to_method.dart b/pkg/analysis_server/lib/src/services/refactoring/convert_getter_to_method.dart
index d1436b8..5c1e88a 100644
--- a/pkg/analysis_server/lib/src/services/refactoring/convert_getter_to_method.dart
+++ b/pkg/analysis_server/lib/src/services/refactoring/convert_getter_to_method.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/protocol_server.dart' hide Element;
 import 'package:analysis_server/src/services/correction/status.dart';
 import 'package:analysis_server/src/services/refactoring/refactoring.dart';
diff --git a/pkg/analysis_server/lib/src/services/refactoring/convert_method_to_getter.dart b/pkg/analysis_server/lib/src/services/refactoring/convert_method_to_getter.dart
index 416e5f2..c1d584c 100644
--- a/pkg/analysis_server/lib/src/services/refactoring/convert_method_to_getter.dart
+++ b/pkg/analysis_server/lib/src/services/refactoring/convert_method_to_getter.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/protocol_server.dart' hide Element;
 import 'package:analysis_server/src/services/correction/status.dart';
 import 'package:analysis_server/src/services/refactoring/refactoring.dart';
diff --git a/pkg/analysis_server/lib/src/services/refactoring/extract_local.dart b/pkg/analysis_server/lib/src/services/refactoring/extract_local.dart
index a582de6..792e05e 100644
--- a/pkg/analysis_server/lib/src/services/refactoring/extract_local.dart
+++ b/pkg/analysis_server/lib/src/services/refactoring/extract_local.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:collection';
 
 import 'package:analysis_server/src/protocol_server.dart' hide Element;
diff --git a/pkg/analysis_server/lib/src/services/refactoring/extract_method.dart b/pkg/analysis_server/lib/src/services/refactoring/extract_method.dart
index 27d1b2b..886804c 100644
--- a/pkg/analysis_server/lib/src/services/refactoring/extract_method.dart
+++ b/pkg/analysis_server/lib/src/services/refactoring/extract_method.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/protocol_server.dart' hide Element;
 import 'package:analysis_server/src/services/correction/name_suggestion.dart';
 import 'package:analysis_server/src/services/correction/selection_analyzer.dart';
diff --git a/pkg/analysis_server/lib/src/services/refactoring/extract_widget.dart b/pkg/analysis_server/lib/src/services/refactoring/extract_widget.dart
index d608269..58adedd5 100644
--- a/pkg/analysis_server/lib/src/services/refactoring/extract_widget.dart
+++ b/pkg/analysis_server/lib/src/services/refactoring/extract_widget.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/protocol_server.dart' hide Element;
 import 'package:analysis_server/src/services/correction/status.dart';
 import 'package:analysis_server/src/services/correction/util.dart';
diff --git a/pkg/analysis_server/lib/src/services/refactoring/inline_local.dart b/pkg/analysis_server/lib/src/services/refactoring/inline_local.dart
index 1ad6b64..0710a92 100644
--- a/pkg/analysis_server/lib/src/services/refactoring/inline_local.dart
+++ b/pkg/analysis_server/lib/src/services/refactoring/inline_local.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/protocol_server.dart' hide Element;
 import 'package:analysis_server/src/services/correction/status.dart';
 import 'package:analysis_server/src/services/correction/util.dart';
diff --git a/pkg/analysis_server/lib/src/services/refactoring/inline_method.dart b/pkg/analysis_server/lib/src/services/refactoring/inline_method.dart
index 00e267f..74b8751 100644
--- a/pkg/analysis_server/lib/src/services/refactoring/inline_method.dart
+++ b/pkg/analysis_server/lib/src/services/refactoring/inline_method.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/protocol_server.dart' hide Element;
 import 'package:analysis_server/src/services/correction/status.dart';
 import 'package:analysis_server/src/services/correction/util.dart';
diff --git a/pkg/analysis_server/lib/src/services/refactoring/move_file.dart b/pkg/analysis_server/lib/src/services/refactoring/move_file.dart
index 614cc5d..9b8bf70 100644
--- a/pkg/analysis_server/lib/src/services/refactoring/move_file.dart
+++ b/pkg/analysis_server/lib/src/services/refactoring/move_file.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:core';
 
 import 'package:analysis_server/src/protocol_server.dart' hide Element;
diff --git a/pkg/analysis_server/lib/src/services/refactoring/refactoring.dart b/pkg/analysis_server/lib/src/services/refactoring/refactoring.dart
index c4220c4..f3c0136 100644
--- a/pkg/analysis_server/lib/src/services/refactoring/refactoring.dart
+++ b/pkg/analysis_server/lib/src/services/refactoring/refactoring.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/services/correction/status.dart';
 import 'package:analysis_server/src/services/refactoring/convert_getter_to_method.dart';
 import 'package:analysis_server/src/services/refactoring/convert_method_to_getter.dart';
diff --git a/pkg/analysis_server/lib/src/services/refactoring/refactoring_internal.dart b/pkg/analysis_server/lib/src/services/refactoring/refactoring_internal.dart
index bb06cec..1677bb8 100644
--- a/pkg/analysis_server/lib/src/services/refactoring/refactoring_internal.dart
+++ b/pkg/analysis_server/lib/src/services/refactoring/refactoring_internal.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:collection';
 
 import 'package:analysis_server/src/protocol_server.dart' hide Element;
diff --git a/pkg/analysis_server/lib/src/services/refactoring/rename.dart b/pkg/analysis_server/lib/src/services/refactoring/rename.dart
index 4e4caef..6c25dd6 100644
--- a/pkg/analysis_server/lib/src/services/refactoring/rename.dart
+++ b/pkg/analysis_server/lib/src/services/refactoring/rename.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/protocol_server.dart' hide Element;
 import 'package:analysis_server/src/services/correction/status.dart';
 import 'package:analysis_server/src/services/correction/util.dart';
diff --git a/pkg/analysis_server/lib/src/services/refactoring/rename_class_member.dart b/pkg/analysis_server/lib/src/services/refactoring/rename_class_member.dart
index 75d6ce5..7cfe3fe 100644
--- a/pkg/analysis_server/lib/src/services/refactoring/rename_class_member.dart
+++ b/pkg/analysis_server/lib/src/services/refactoring/rename_class_member.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/protocol_server.dart'
     hide Element, ElementKind;
 import 'package:analysis_server/src/services/correction/status.dart';
diff --git a/pkg/analysis_server/lib/src/services/refactoring/rename_constructor.dart b/pkg/analysis_server/lib/src/services/refactoring/rename_constructor.dart
index 1ea0e0d..1009de9 100644
--- a/pkg/analysis_server/lib/src/services/refactoring/rename_constructor.dart
+++ b/pkg/analysis_server/lib/src/services/refactoring/rename_constructor.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/protocol_server.dart' hide Element;
 import 'package:analysis_server/src/services/correction/status.dart';
 import 'package:analysis_server/src/services/correction/util.dart';
diff --git a/pkg/analysis_server/lib/src/services/refactoring/rename_extension_member.dart b/pkg/analysis_server/lib/src/services/refactoring/rename_extension_member.dart
index 700f7cf..3a4a3a5 100644
--- a/pkg/analysis_server/lib/src/services/refactoring/rename_extension_member.dart
+++ b/pkg/analysis_server/lib/src/services/refactoring/rename_extension_member.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/protocol_server.dart'
     hide Element, ElementKind;
 import 'package:analysis_server/src/services/correction/status.dart';
diff --git a/pkg/analysis_server/lib/src/services/refactoring/rename_import.dart b/pkg/analysis_server/lib/src/services/refactoring/rename_import.dart
index 1183fcc..0dfbac5 100644
--- a/pkg/analysis_server/lib/src/services/refactoring/rename_import.dart
+++ b/pkg/analysis_server/lib/src/services/refactoring/rename_import.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/protocol_server.dart';
 import 'package:analysis_server/src/services/correction/status.dart';
 import 'package:analysis_server/src/services/refactoring/naming_conventions.dart';
diff --git a/pkg/analysis_server/lib/src/services/refactoring/rename_label.dart b/pkg/analysis_server/lib/src/services/refactoring/rename_label.dart
index cebd04e..d32922a 100644
--- a/pkg/analysis_server/lib/src/services/refactoring/rename_label.dart
+++ b/pkg/analysis_server/lib/src/services/refactoring/rename_label.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/services/correction/status.dart';
 import 'package:analysis_server/src/services/refactoring/naming_conventions.dart';
 import 'package:analysis_server/src/services/refactoring/refactoring.dart';
diff --git a/pkg/analysis_server/lib/src/services/refactoring/rename_library.dart b/pkg/analysis_server/lib/src/services/refactoring/rename_library.dart
index f6eaa71..68b8849 100644
--- a/pkg/analysis_server/lib/src/services/refactoring/rename_library.dart
+++ b/pkg/analysis_server/lib/src/services/refactoring/rename_library.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/services/correction/status.dart';
 import 'package:analysis_server/src/services/refactoring/naming_conventions.dart';
 import 'package:analysis_server/src/services/refactoring/refactoring.dart';
diff --git a/pkg/analysis_server/lib/src/services/refactoring/rename_local.dart b/pkg/analysis_server/lib/src/services/refactoring/rename_local.dart
index 386496d..3b3d492 100644
--- a/pkg/analysis_server/lib/src/services/refactoring/rename_local.dart
+++ b/pkg/analysis_server/lib/src/services/refactoring/rename_local.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/protocol_server.dart'
     hide Element, ElementKind;
 import 'package:analysis_server/src/services/correction/status.dart';
diff --git a/pkg/analysis_server/lib/src/services/refactoring/rename_unit_member.dart b/pkg/analysis_server/lib/src/services/refactoring/rename_unit_member.dart
index b8d9705..0838f89 100644
--- a/pkg/analysis_server/lib/src/services/refactoring/rename_unit_member.dart
+++ b/pkg/analysis_server/lib/src/services/refactoring/rename_unit_member.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/protocol_server.dart'
     show newLocation_fromElement, newLocation_fromMatch;
 import 'package:analysis_server/src/services/correction/status.dart';
diff --git a/pkg/analysis_server/lib/src/services/search/hierarchy.dart b/pkg/analysis_server/lib/src/services/search/hierarchy.dart
index 9f600f3..7a3f90e 100644
--- a/pkg/analysis_server/lib/src/services/search/hierarchy.dart
+++ b/pkg/analysis_server/lib/src/services/search/hierarchy.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:collection';
 
 import 'package:analysis_server/src/services/search/element_visitors.dart';
diff --git a/pkg/analysis_server/lib/src/services/search/search_engine.dart b/pkg/analysis_server/lib/src/services/search/search_engine.dart
index 75beef9d..95b74ec 100644
--- a/pkg/analysis_server/lib/src/services/search/search_engine.dart
+++ b/pkg/analysis_server/lib/src/services/search/search_engine.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/src/generated/source.dart';
 
diff --git a/pkg/analysis_server/lib/src/services/search/search_engine_internal.dart b/pkg/analysis_server/lib/src/services/search/search_engine_internal.dart
index b680a98..49b10c9 100644
--- a/pkg/analysis_server/lib/src/services/search/search_engine_internal.dart
+++ b/pkg/analysis_server/lib/src/services/search/search_engine_internal.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/services/search/search_engine.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/src/dart/analysis/driver.dart';
diff --git a/pkg/analysis_server/lib/src/status/diagnostics.dart b/pkg/analysis_server/lib/src/status/diagnostics.dart
index d2680b1..dcbc8f0 100644
--- a/pkg/analysis_server/lib/src/status/diagnostics.dart
+++ b/pkg/analysis_server/lib/src/status/diagnostics.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:developer' as developer;
 import 'dart:io';
 
diff --git a/pkg/analysis_server/lib/src/status/pages.dart b/pkg/analysis_server/lib/src/status/pages.dart
index 795b8c9..177f04f 100644
--- a/pkg/analysis_server/lib/src/status/pages.dart
+++ b/pkg/analysis_server/lib/src/status/pages.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
diff --git a/pkg/analysis_server/lib/src/utilities/profiling.dart b/pkg/analysis_server/lib/src/utilities/profiling.dart
index 7de48e8..1d18313 100644
--- a/pkg/analysis_server/lib/src/utilities/profiling.dart
+++ b/pkg/analysis_server/lib/src/utilities/profiling.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:io';
 
 /// A class that can return memory and cpu usage information for a given
diff --git a/pkg/analysis_server/test/abstract_context.dart b/pkg/analysis_server/test/abstract_context.dart
index d890e91..7a99a5e 100644
--- a/pkg/analysis_server/test/abstract_context.dart
+++ b/pkg/analysis_server/test/abstract_context.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/dart/analysis/analysis_context.dart';
 import 'package:analyzer/dart/analysis/analysis_context_collection.dart';
 import 'package:analyzer/dart/analysis/session.dart';
diff --git a/pkg/analysis_server/test/abstract_single_unit.dart b/pkg/analysis_server/test/abstract_single_unit.dart
index c6e2124..5b10d92 100644
--- a/pkg/analysis_server/test/abstract_single_unit.dart
+++ b/pkg/analysis_server/test/abstract_single_unit.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/dart/analysis/results.dart';
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
diff --git a/pkg/analysis_server/test/analysis/get_errors_test.dart b/pkg/analysis_server/test/analysis/get_errors_test.dart
index d6f4ef2..5707925 100644
--- a/pkg/analysis_server/test/analysis/get_errors_test.dart
+++ b/pkg/analysis_server/test/analysis/get_errors_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol.dart';
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analysis_server/src/domain_analysis.dart';
diff --git a/pkg/analysis_server/test/analysis/get_hover_test.dart b/pkg/analysis_server/test/analysis/get_hover_test.dart
index c214da5..060a52a 100644
--- a/pkg/analysis_server/test/analysis/get_hover_test.dart
+++ b/pkg/analysis_server/test/analysis/get_hover_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
diff --git a/pkg/analysis_server/test/analysis/get_signature_test.dart b/pkg/analysis_server/test/analysis/get_signature_test.dart
index 24a954c..0579563 100644
--- a/pkg/analysis_server/test/analysis/get_signature_test.dart
+++ b/pkg/analysis_server/test/analysis/get_signature_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol.dart';
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analysis_server/src/protocol_server.dart';
diff --git a/pkg/analysis_server/test/analysis/notification_analyzed_files_test.dart b/pkg/analysis_server/test/analysis/notification_analyzed_files_test.dart
index 4c14ff0..c574991 100644
--- a/pkg/analysis_server/test/analysis/notification_analyzed_files_test.dart
+++ b/pkg/analysis_server/test/analysis/notification_analyzed_files_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol.dart';
 import 'package:analysis_server/protocol/protocol_constants.dart';
 import 'package:analysis_server/protocol/protocol_generated.dart';
diff --git a/pkg/analysis_server/test/analysis/notification_implemented_test.dart b/pkg/analysis_server/test/analysis/notification_implemented_test.dart
index 2c0ab59..43a5a24 100644
--- a/pkg/analysis_server/test/analysis/notification_implemented_test.dart
+++ b/pkg/analysis_server/test/analysis/notification_implemented_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol.dart';
 import 'package:analysis_server/protocol/protocol_constants.dart';
 import 'package:analysis_server/protocol/protocol_generated.dart';
diff --git a/pkg/analysis_server/test/analysis_abstract.dart b/pkg/analysis_server/test/analysis_abstract.dart
index 6603372..8a90649 100644
--- a/pkg/analysis_server/test/analysis_abstract.dart
+++ b/pkg/analysis_server/test/analysis_abstract.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol.dart';
 import 'package:analysis_server/protocol/protocol_constants.dart';
 import 'package:analysis_server/protocol/protocol_generated.dart'
diff --git a/pkg/analysis_server/test/analysis_server_test.dart b/pkg/analysis_server/test/analysis_server_test.dart
index e0bd3d6..f99570b 100644
--- a/pkg/analysis_server/test/analysis_server_test.dart
+++ b/pkg/analysis_server/test/analysis_server_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol.dart';
 import 'package:analysis_server/protocol/protocol_constants.dart';
 import 'package:analysis_server/protocol/protocol_generated.dart';
diff --git a/pkg/analysis_server/test/client/impl/abstract_client.dart b/pkg/analysis_server/test/client/impl/abstract_client.dart
index f5ea242..a8613f8 100644
--- a/pkg/analysis_server/test/client/impl/abstract_client.dart
+++ b/pkg/analysis_server/test/client/impl/abstract_client.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol.dart';
 import 'package:analysis_server/protocol/protocol_generated.dart'
     hide AnalysisOptions;
diff --git a/pkg/analysis_server/test/completion_test.dart b/pkg/analysis_server/test/completion_test.dart
index f5f37f4..ec1e2e4 100644
--- a/pkg/analysis_server/test/completion_test.dart
+++ b/pkg/analysis_server/test/completion_test.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:collection';
 
 import 'package:test/test.dart';
diff --git a/pkg/analysis_server/test/completion_test_support.dart b/pkg/analysis_server/test/completion_test_support.dart
index 83660df..2221945 100644
--- a/pkg/analysis_server/test/completion_test_support.dart
+++ b/pkg/analysis_server/test/completion_test_support.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:collection';
 
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
diff --git a/pkg/analysis_server/test/context_manager_test.dart b/pkg/analysis_server/test/context_manager_test.dart
index b7fbb8b..0669678 100644
--- a/pkg/analysis_server/test/context_manager_test.dart
+++ b/pkg/analysis_server/test/context_manager_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/context_manager.dart';
 import 'package:analysis_server/src/plugin/notification_manager.dart';
 import 'package:analysis_server/src/utilities/null_string_sink.dart';
diff --git a/pkg/analysis_server/test/domain_completion_test.dart b/pkg/analysis_server/test/domain_completion_test.dart
index 715556b..9bae3c4 100644
--- a/pkg/analysis_server/test/domain_completion_test.dart
+++ b/pkg/analysis_server/test/domain_completion_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analysis_server/src/plugin/plugin_manager.dart';
 import 'package:analysis_server/src/provisional/completion/completion_core.dart';
diff --git a/pkg/analysis_server/test/edit/assists_test.dart b/pkg/analysis_server/test/edit/assists_test.dart
index 5db8580..438a81e 100644
--- a/pkg/analysis_server/test/edit/assists_test.dart
+++ b/pkg/analysis_server/test/edit/assists_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analysis_server/src/edit/edit_domain.dart';
 import 'package:analysis_server/src/plugin/plugin_manager.dart';
diff --git a/pkg/analysis_server/test/edit/bulk_fixes_test.dart b/pkg/analysis_server/test/edit/bulk_fixes_test.dart
index d72f623..c1d8b75 100644
--- a/pkg/analysis_server/test/edit/bulk_fixes_test.dart
+++ b/pkg/analysis_server/test/edit/bulk_fixes_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analysis_server/src/edit/edit_domain.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
diff --git a/pkg/analysis_server/test/edit/fixes_test.dart b/pkg/analysis_server/test/edit/fixes_test.dart
index 738501c..7de1b0d 100644
--- a/pkg/analysis_server/test/edit/fixes_test.dart
+++ b/pkg/analysis_server/test/edit/fixes_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analysis_server/src/edit/edit_domain.dart';
 import 'package:analysis_server/src/plugin/plugin_manager.dart';
diff --git a/pkg/analysis_server/test/edit/format_test.dart b/pkg/analysis_server/test/edit/format_test.dart
index 8759121..ac5b566 100644
--- a/pkg/analysis_server/test/edit/format_test.dart
+++ b/pkg/analysis_server/test/edit/format_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analysis_server/src/edit/edit_domain.dart';
 import 'package:test/test.dart';
diff --git a/pkg/analysis_server/test/edit/organize_directives_test.dart b/pkg/analysis_server/test/edit/organize_directives_test.dart
index 618c6d6..4a775db 100644
--- a/pkg/analysis_server/test/edit/organize_directives_test.dart
+++ b/pkg/analysis_server/test/edit/organize_directives_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analysis_server/src/edit/edit_domain.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
diff --git a/pkg/analysis_server/test/edit/refactoring_test.dart b/pkg/analysis_server/test/edit/refactoring_test.dart
index acf5f34..6da76ec 100644
--- a/pkg/analysis_server/test/edit/refactoring_test.dart
+++ b/pkg/analysis_server/test/edit/refactoring_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol.dart';
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analysis_server/src/edit/edit_domain.dart';
diff --git a/pkg/analysis_server/test/edit/sort_members_test.dart b/pkg/analysis_server/test/edit/sort_members_test.dart
index 94d0659..bd226a2 100644
--- a/pkg/analysis_server/test/edit/sort_members_test.dart
+++ b/pkg/analysis_server/test/edit/sort_members_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analysis_server/src/edit/edit_domain.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
diff --git a/pkg/analysis_server/test/integration/analysis/get_errors_non_standard_sdk_test.dart b/pkg/analysis_server/test/integration/analysis/get_errors_non_standard_sdk_test.dart
index f1fd49a..477e325 100644
--- a/pkg/analysis_server/test/integration/analysis/get_errors_non_standard_sdk_test.dart
+++ b/pkg/analysis_server/test/integration/analysis/get_errors_non_standard_sdk_test.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:io';
 
 import 'package:path/path.dart' as path;
diff --git a/pkg/analysis_server/test/integration/analysis/get_hover_test.dart b/pkg/analysis_server/test/integration/analysis/get_hover_test.dart
index 9458086..18b3976 100644
--- a/pkg/analysis_server/test/integration/analysis/get_hover_test.dart
+++ b/pkg/analysis_server/test/integration/analysis/get_hover_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:path/path.dart' as path;
 import 'package:test/test.dart';
diff --git a/pkg/analysis_server/test/integration/analysis/get_imported_elements_test.dart b/pkg/analysis_server/test/integration/analysis/get_imported_elements_test.dart
index 9c87374..436da25 100644
--- a/pkg/analysis_server/test/integration/analysis/get_imported_elements_test.dart
+++ b/pkg/analysis_server/test/integration/analysis/get_imported_elements_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analysis_server/src/domain_analysis.dart';
 import 'package:path/path.dart' as path;
diff --git a/pkg/analysis_server/test/integration/analysis/highlights2_test.dart b/pkg/analysis_server/test/integration/analysis/highlights2_test.dart
index 93c8a9e..0e1da88 100644
--- a/pkg/analysis_server/test/integration/analysis/highlights2_test.dart
+++ b/pkg/analysis_server/test/integration/analysis/highlights2_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
 import 'package:test/test.dart';
diff --git a/pkg/analysis_server/test/integration/analysis/package_root_test.dart b/pkg/analysis_server/test/integration/analysis/package_root_test.dart
index f3cac4b..3bb2096 100644
--- a/pkg/analysis_server/test/integration/analysis/package_root_test.dart
+++ b/pkg/analysis_server/test/integration/analysis/package_root_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
 import 'package:path/path.dart' as path;
diff --git a/pkg/analysis_server/test/integration/analysis/reanalyze_concurrent_test.dart b/pkg/analysis_server/test/integration/analysis/reanalyze_concurrent_test.dart
index 08eb92d..1a42362 100644
--- a/pkg/analysis_server/test/integration/analysis/reanalyze_concurrent_test.dart
+++ b/pkg/analysis_server/test/integration/analysis/reanalyze_concurrent_test.dart
@@ -6,8 +6,6 @@
 /// progress, no problems occur.
 ///
 /// See dartbug.com/21448.
-import 'dart:async';
-
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
diff --git a/pkg/analysis_server/test/integration/edit/import_elements_test.dart b/pkg/analysis_server/test/integration/edit/import_elements_test.dart
index f717356..06ab05f 100644
--- a/pkg/analysis_server/test/integration/edit/import_elements_test.dart
+++ b/pkg/analysis_server/test/integration/edit/import_elements_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analyzer/file_system/physical_file_system.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
diff --git a/pkg/analysis_server/test/integration/search/find_element_references_test.dart b/pkg/analysis_server/test/integration/search/find_element_references_test.dart
index 222d0dc..c0d758a 100644
--- a/pkg/analysis_server/test/integration/search/find_element_references_test.dart
+++ b/pkg/analysis_server/test/integration/search/find_element_references_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
diff --git a/pkg/analysis_server/test/integration/search/get_type_hierarchy_test.dart b/pkg/analysis_server/test/integration/search/get_type_hierarchy_test.dart
index ceaf72d..0003214 100644
--- a/pkg/analysis_server/test/integration/search/get_type_hierarchy_test.dart
+++ b/pkg/analysis_server/test/integration/search/get_type_hierarchy_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
 import 'package:test/test.dart';
diff --git a/pkg/analysis_server/test/integration/server/shutdown_test.dart b/pkg/analysis_server/test/integration/server/shutdown_test.dart
index e43a0b0..a14e573 100644
--- a/pkg/analysis_server/test/integration/server/shutdown_test.dart
+++ b/pkg/analysis_server/test/integration/server/shutdown_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
diff --git a/pkg/analysis_server/test/lsp/change_workspace_folders_test.dart b/pkg/analysis_server/test/lsp/change_workspace_folders_test.dart
index ef38052..3b42924 100644
--- a/pkg/analysis_server/test/lsp/change_workspace_folders_test.dart
+++ b/pkg/analysis_server/test/lsp/change_workspace_folders_test.dart
@@ -59,6 +59,139 @@
     );
   }
 
+  Future<void>
+      test_changeWorkspaceFolders_addExplicitParentOfImplicit_closeFile() async {
+    final nestedFolderPath =
+        join(workspaceFolder1Path, 'nested', 'deeply', 'in', 'folders');
+    final nestedFilePath = join(nestedFolderPath, 'test.dart');
+    final nestedFileUri = Uri.file(nestedFilePath);
+    await newFile(nestedFilePath);
+
+    await initialize(allowEmptyRootUri: true);
+    await openFile(nestedFileUri, '');
+
+    // Expect implicit root for the open file.
+    expect(
+      server.contextManager.includedPaths,
+      unorderedEquals([nestedFolderPath]),
+    );
+
+    // Add the real project root to the workspace (which should become an
+    // explicit root).
+    await changeWorkspaceFolders(add: [workspaceFolder1Uri]);
+    expect(
+      server.contextManager.includedPaths,
+      unorderedEquals([workspaceFolder1Path, nestedFolderPath]),
+    );
+
+    // Closing the file should not result in the project being removed.
+    await closeFile(nestedFileUri);
+    expect(
+      server.contextManager.includedPaths,
+      unorderedEquals([workspaceFolder1Path]),
+    );
+  }
+
+  Future<void>
+      test_changeWorkspaceFolders_addExplicitParentOfImplicit_closeFolder() async {
+    final nestedFolderPath =
+        join(workspaceFolder1Path, 'nested', 'deeply', 'in', 'folders');
+    final nestedFilePath = join(nestedFolderPath, 'test.dart');
+    final nestedFileUri = Uri.file(nestedFilePath);
+    await newFile(nestedFilePath);
+
+    await initialize(allowEmptyRootUri: true);
+    await openFile(nestedFileUri, '');
+
+    // Expect implicit root for the open file.
+    expect(
+      server.contextManager.includedPaths,
+      unorderedEquals([nestedFolderPath]),
+    );
+
+    // Add the real project root to the workspace (which should become an
+    // explicit root).
+    await changeWorkspaceFolders(add: [workspaceFolder1Uri]);
+    expect(
+      server.contextManager.includedPaths,
+      unorderedEquals([workspaceFolder1Path, nestedFolderPath]),
+    );
+
+    // Removing the workspace folder should result in falling back to just the
+    // nested folder.
+    await changeWorkspaceFolders(remove: [workspaceFolder1Uri]);
+    expect(
+      server.contextManager.includedPaths,
+      unorderedEquals([nestedFolderPath]),
+    );
+  }
+
+  Future<void>
+      test_changeWorkspaceFolders_addImplicitChildOfExplicitParent_closeFile() async {
+    final nestedFolderPath =
+        join(workspaceFolder1Path, 'nested', 'deeply', 'in', 'folders');
+    final nestedFilePath = join(nestedFolderPath, 'test.dart');
+    final nestedFileUri = Uri.file(nestedFilePath);
+    await newFile(nestedFilePath);
+
+    await initialize(workspaceFolders: [workspaceFolder1Uri]);
+
+    // Expect explicit root for the workspace folder.
+    expect(
+      server.contextManager.includedPaths,
+      unorderedEquals([workspaceFolder1Path]),
+    );
+
+    // Open a file, though no new root is expected as it was mapped to the existing
+    // open folder.
+    await openFile(nestedFileUri, '');
+    expect(
+      server.contextManager.includedPaths,
+      unorderedEquals([workspaceFolder1Path]),
+    );
+
+    // Closing the file should not result in the project being removed.
+    await closeFile(nestedFileUri);
+    expect(
+      server.contextManager.includedPaths,
+      unorderedEquals([workspaceFolder1Path]),
+    );
+  }
+
+  Future<void>
+      test_changeWorkspaceFolders_addImplicitChildOfExplicitParent_closeFolder() async {
+    final nestedFolderPath =
+        join(workspaceFolder1Path, 'nested', 'deeply', 'in', 'folders');
+    final nestedFilePath = join(nestedFolderPath, 'test.dart');
+    final nestedFileUri = Uri.file(nestedFilePath);
+    await newFile(nestedFilePath);
+
+    await initialize(workspaceFolders: [workspaceFolder1Uri]);
+
+    // Expect explicit root for the workspace folder.
+    expect(
+      server.contextManager.includedPaths,
+      unorderedEquals([workspaceFolder1Path]),
+    );
+
+    // Open a file, though no new root is expected as it was mapped to the existing
+    // open folder.
+    await openFile(nestedFileUri, '');
+    expect(
+      server.contextManager.includedPaths,
+      unorderedEquals([workspaceFolder1Path]),
+    );
+
+    // Removing the workspace folder will retain the workspace folder, as that's
+    // the folder we picked when the file was opened since there was already
+    // a root for it.
+    await changeWorkspaceFolders(remove: [workspaceFolder1Uri]);
+    expect(
+      server.contextManager.includedPaths,
+      unorderedEquals([workspaceFolder1Path]),
+    );
+  }
+
   Future<void> test_changeWorkspaceFolders_remove() async {
     await initialize(
       workspaceFolders: [workspaceFolder1Uri, workspaceFolder2Uri],
@@ -79,7 +212,7 @@
 
     // Generate an error in the test project.
     final firstDiagnosticsUpdate = waitForDiagnostics(mainFileUri);
-    await openFile(mainFileUri, 'String a = 1;');
+    newFile(mainFilePath, content: 'String a = 1;');
     final initialDiagnostics = await firstDiagnosticsUpdate;
     expect(initialDiagnostics, hasLength(1));
 
diff --git a/pkg/analysis_server/test/lsp/configuration_test.dart b/pkg/analysis_server/test/lsp/configuration_test.dart
index e49d54e..16ea16e 100644
--- a/pkg/analysis_server/test/lsp/configuration_test.dart
+++ b/pkg/analysis_server/test/lsp/configuration_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/lsp_protocol/protocol_generated.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
diff --git a/pkg/analysis_server/test/lsp/document_symbols_test.dart b/pkg/analysis_server/test/lsp/document_symbols_test.dart
index 8ba455a..e571578 100644
--- a/pkg/analysis_server/test/lsp/document_symbols_test.dart
+++ b/pkg/analysis_server/test/lsp/document_symbols_test.dart
@@ -3,9 +3,11 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analysis_server/lsp_protocol/protocol_generated.dart';
+import 'package:analysis_server/src/lsp/constants.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
+import '../tool/lsp_spec/matchers.dart';
 import 'server_abstract.dart';
 
 void main() {
@@ -115,6 +117,38 @@
     expect(method.kind, equals(SymbolKind.Method));
   }
 
+  Future<void> test_noAnalysisRoot_openedFile() async {
+    // When there are no analysis roots and we open a file, it should be added as
+    // a temporary root allowing us to service requests for it.
+    const content = 'class MyClass {}';
+    newFile(mainFilePath, content: content);
+    await initialize(allowEmptyRootUri: true);
+    await openFile(mainFileUri, content);
+
+    final result = await getDocumentSymbols(mainFileUri.toString());
+    final symbols = result.map(
+      (docsymbols) => throw 'Expected SymbolInformations, got DocumentSymbols',
+      (symbolInfos) => symbolInfos,
+    );
+    expect(symbols, hasLength(1));
+
+    final myClass = symbols[0];
+    expect(myClass.name, equals('MyClass'));
+    expect(myClass.kind, equals(SymbolKind.Class));
+    expect(myClass.containerName, isNull);
+  }
+
+  Future<void> test_noAnalysisRoot_unopenedFile() async {
+    // When there are no analysis roots and we receive requests for a file that
+    // was not opened, we will reject the file due to not being analyzed.
+    const content = 'class MyClass {}';
+    newFile(mainFilePath, content: content);
+    await initialize(allowEmptyRootUri: true);
+
+    await expectLater(getDocumentSymbols(mainFileUri.toString()),
+        throwsA(isResponseError(ServerErrorCodes.InvalidFilePath)));
+  }
+
   Future<void> test_nonDartFile() async {
     newFile(pubspecFilePath, content: simplePubspecContent);
     await initialize();
diff --git a/pkg/analysis_server/test/lsp/initialization_test.dart b/pkg/analysis_server/test/lsp/initialization_test.dart
index f8bf3d6..72596b7 100644
--- a/pkg/analysis_server/test/lsp/initialization_test.dart
+++ b/pkg/analysis_server/test/lsp/initialization_test.dart
@@ -7,6 +7,7 @@
 import 'package:analysis_server/src/lsp/constants.dart';
 import 'package:analysis_server/src/lsp/server_capabilities_computer.dart';
 import 'package:analysis_server/src/plugin/plugin_manager.dart';
+import 'package:path/path.dart' as path;
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
@@ -256,6 +257,78 @@
     );
   }
 
+  Future<void> test_emptyAnalysisRoots_multipleOpenFiles() async {
+    final file1 = join(projectFolderPath, 'file1.dart');
+    final file1Uri = Uri.file(file1);
+    await newFile(file1);
+    final file2 = join(projectFolderPath, 'file2.dart');
+    final file2Uri = Uri.file(file2);
+    await newFile(file2);
+    final pubspecPath = join(projectFolderPath, 'pubspec.yaml');
+    await newFile(pubspecPath);
+
+    await initialize(allowEmptyRootUri: true);
+
+    // Opening both files should only add the project folder once.
+    await openFile(file1Uri, '');
+    await openFile(file2Uri, '');
+    expect(server.contextManager.includedPaths, equals([projectFolderPath]));
+
+    // Closing only one of the files should not remove the project folder
+    // since there are still open files.
+    await closeFile(file1Uri);
+    expect(server.contextManager.includedPaths, equals([projectFolderPath]));
+
+    // Closing the last file should remove the project folder.
+    await closeFile(file2Uri);
+    expect(server.contextManager.includedPaths, equals([]));
+  }
+
+  Future<void> test_emptyAnalysisRoots_projectWithoutPubspec() async {
+    final nestedFilePath = join(
+        projectFolderPath, 'nested', 'deeply', 'in', 'folders', 'test.dart');
+    final nestedFileUri = Uri.file(nestedFilePath);
+    await newFile(nestedFilePath);
+
+    // The project folder shouldn't be added to start with.
+    await initialize(allowEmptyRootUri: true);
+    expect(server.contextManager.includedPaths, equals([]));
+
+    // Opening the file should trigger the immediate parent folder to be added.
+    await openFile(nestedFileUri, '');
+    expect(server.contextManager.includedPaths,
+        equals([path.dirname(nestedFilePath)]));
+  }
+
+  Future<void> test_emptyAnalysisRoots_projectWithPubspec() async {
+    final nestedFilePath = join(
+        projectFolderPath, 'nested', 'deeply', 'in', 'folders', 'test.dart');
+    final nestedFileUri = Uri.file(nestedFilePath);
+    await newFile(nestedFilePath);
+    final pubspecPath = join(projectFolderPath, 'pubspec.yaml');
+    await newFile(pubspecPath);
+
+    // The project folder shouldn't be added to start with.
+    await initialize(allowEmptyRootUri: true);
+    expect(server.contextManager.includedPaths, equals([]));
+
+    // Opening a file nested within the project should add the project folder.
+    await openFile(nestedFileUri, '');
+    expect(server.contextManager.includedPaths, equals([projectFolderPath]));
+
+    // Ensure the file was cached in each driver. This happens as a result of
+    // adding to priority files, but if that's done before the file is in an
+    // analysis root it will not occur.
+    // https://github.com/dart-lang/sdk/issues/37338
+    server.driverMap.values.forEach((driver) {
+      expect(driver.getCachedResult(nestedFilePath), isNotNull);
+    });
+
+    // Closing the file should remove it.
+    await closeFile(nestedFileUri);
+    expect(server.contextManager.includedPaths, equals([]));
+  }
+
   Future<void> test_initialize() async {
     final response = await initialize();
     expect(response, isNotNull);
@@ -360,16 +433,10 @@
     );
     expect(server.contextManager.includedPaths, equals([]));
 
-    // Opening a file nested within the project will still not add the project
-    // folder because there was no pubspec.
-    final messageFromServer = await expectNotification<ShowMessageParams>(
-      (notification) => notification.method == Method.window_showMessage,
-      () => openFile(nestedFileUri, ''),
-    );
-    expect(server.contextManager.includedPaths, equals([]));
-    expect(messageFromServer.type, MessageType.Warning);
-    expect(messageFromServer.message,
-        contains('using onlyAnalyzeProjectsWithOpenFiles'));
+    // Opening the file should trigger the immediate parent folder to be added.
+    await openFile(nestedFileUri, '');
+    expect(server.contextManager.includedPaths,
+        equals([path.dirname(nestedFilePath)]));
   }
 
   Future<void> test_onlyAnalyzeProjectsWithOpenFiles_withPubpsec() async {
diff --git a/pkg/analysis_server/test/lsp/server_abstract.dart b/pkg/analysis_server/test/lsp/server_abstract.dart
index b2d873c..899b399 100644
--- a/pkg/analysis_server/test/lsp/server_abstract.dart
+++ b/pkg/analysis_server/test/lsp/server_abstract.dart
@@ -896,10 +896,14 @@
     ClientCapabilitiesWindow windowCapabilities,
     Map<String, Object> initializationOptions,
     bool throwOnFailure = true,
+    bool allowEmptyRootUri = false,
   }) async {
     // Assume if none of the project options were set, that we want to default to
     // opening the test project folder.
-    if (rootPath == null && rootUri == null && workspaceFolders == null) {
+    if (rootPath == null &&
+        rootUri == null &&
+        workspaceFolders == null &&
+        !allowEmptyRootUri) {
       rootUri = Uri.file(projectFolderPath);
     }
     final request = makeRequest(
diff --git a/pkg/analysis_server/test/search/abstract_search_domain.dart b/pkg/analysis_server/test/search/abstract_search_domain.dart
index faa06b0..1e5b0d1 100644
--- a/pkg/analysis_server/test/search/abstract_search_domain.dart
+++ b/pkg/analysis_server/test/search/abstract_search_domain.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol.dart';
 import 'package:analysis_server/protocol/protocol_constants.dart';
 import 'package:analysis_server/protocol/protocol_generated.dart';
diff --git a/pkg/analysis_server/test/search/declarations_test.dart b/pkg/analysis_server/test/search/declarations_test.dart
index 88ebb33..cb79730 100644
--- a/pkg/analysis_server/test/search/declarations_test.dart
+++ b/pkg/analysis_server/test/search/declarations_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
 import 'package:test/test.dart';
diff --git a/pkg/analysis_server/test/search/element_references_test.dart b/pkg/analysis_server/test/search/element_references_test.dart
index 12d5198..342dc7c 100644
--- a/pkg/analysis_server/test/search/element_references_test.dart
+++ b/pkg/analysis_server/test/search/element_references_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
 import 'package:test/test.dart';
diff --git a/pkg/analysis_server/test/search/member_declarations_test.dart b/pkg/analysis_server/test/search/member_declarations_test.dart
index 5b213e9..5e02cc2 100644
--- a/pkg/analysis_server/test/search/member_declarations_test.dart
+++ b/pkg/analysis_server/test/search/member_declarations_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
 import 'package:test/test.dart';
diff --git a/pkg/analysis_server/test/search/member_references_test.dart b/pkg/analysis_server/test/search/member_references_test.dart
index 9438381..a2c7b18 100644
--- a/pkg/analysis_server/test/search/member_references_test.dart
+++ b/pkg/analysis_server/test/search/member_references_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
diff --git a/pkg/analysis_server/test/search/top_level_declarations_test.dart b/pkg/analysis_server/test/search/top_level_declarations_test.dart
index a3f5ed3..84735c2 100644
--- a/pkg/analysis_server/test/search/top_level_declarations_test.dart
+++ b/pkg/analysis_server/test/search/top_level_declarations_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
 import 'package:test/test.dart';
diff --git a/pkg/analysis_server/test/search/type_hierarchy_test.dart b/pkg/analysis_server/test/search/type_hierarchy_test.dart
index 618f5b9..2c0f034 100644
--- a/pkg/analysis_server/test/search/type_hierarchy_test.dart
+++ b/pkg/analysis_server/test/search/type_hierarchy_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol.dart';
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analysis_server/src/search/search_domain.dart';
diff --git a/pkg/analysis_server/test/services/completion/dart/common_usage_sorter_test.dart b/pkg/analysis_server/test/services/completion/dart/common_usage_sorter_test.dart
index 2edf873..c8d2ae5 100644
--- a/pkg/analysis_server/test/services/completion/dart/common_usage_sorter_test.dart
+++ b/pkg/analysis_server/test/services/completion/dart/common_usage_sorter_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/completion/dart/common_usage_sorter.dart';
 import 'package:analysis_server/src/services/completion/dart/completion_manager.dart';
diff --git a/pkg/analysis_server/test/services/completion/dart/type_member_contributor_test.dart b/pkg/analysis_server/test/services/completion/dart/type_member_contributor_test.dart
index 2d7372c..ba212b20 100644
--- a/pkg/analysis_server/test/services/completion/dart/type_member_contributor_test.dart
+++ b/pkg/analysis_server/test/services/completion/dart/type_member_contributor_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/completion/dart/type_member_contributor.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
diff --git a/pkg/analysis_server/test/services/completion/postfix/postfix_completion_test.dart b/pkg/analysis_server/test/services/completion/postfix/postfix_completion_test.dart
index ec15e1d..44c2b39 100644
--- a/pkg/analysis_server/test/services/completion/postfix/postfix_completion_test.dart
+++ b/pkg/analysis_server/test/services/completion/postfix/postfix_completion_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/protocol_server.dart';
 import 'package:analysis_server/src/services/completion/postfix/postfix_completion.dart';
 import 'package:test/test.dart';
diff --git a/pkg/analysis_server/test/services/correction/organize_directives_test.dart b/pkg/analysis_server/test/services/correction/organize_directives_test.dart
index 77ab9c2..3ce8fbc 100644
--- a/pkg/analysis_server/test/services/correction/organize_directives_test.dart
+++ b/pkg/analysis_server/test/services/correction/organize_directives_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/services/correction/organize_imports.dart';
 import 'package:analyzer/error/error.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart'
diff --git a/pkg/analysis_server/test/services/correction/sort_members_test.dart b/pkg/analysis_server/test/services/correction/sort_members_test.dart
index 43174c5c..64d74cc 100644
--- a/pkg/analysis_server/test/services/correction/sort_members_test.dart
+++ b/pkg/analysis_server/test/services/correction/sort_members_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/services/correction/sort_members.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
 import 'package:test/test.dart';
diff --git a/pkg/analysis_server/test/services/correction/util_test.dart b/pkg/analysis_server/test/services/correction/util_test.dart
index 31dfce9..530c5ea 100644
--- a/pkg/analysis_server/test/services/correction/util_test.dart
+++ b/pkg/analysis_server/test/services/correction/util_test.dart
@@ -1,7 +1,6 @@
 // Copyright (c) 2016, the Dart project authors. Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
-import 'dart:async';
 
 import 'package:analysis_server/src/services/correction/util.dart';
 import 'package:analyzer/dart/ast/ast.dart';
diff --git a/pkg/analysis_server/test/services/refactoring/abstract_refactoring.dart b/pkg/analysis_server/test/services/refactoring/abstract_refactoring.dart
index 640868c..1353f6d 100644
--- a/pkg/analysis_server/test/services/refactoring/abstract_refactoring.dart
+++ b/pkg/analysis_server/test/services/refactoring/abstract_refactoring.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/services/correction/status.dart';
 import 'package:analysis_server/src/services/refactoring/refactoring.dart';
 import 'package:analysis_server/src/services/search/search_engine.dart';
diff --git a/pkg/analysis_server/test/services/refactoring/convert_getter_to_method_test.dart b/pkg/analysis_server/test/services/refactoring/convert_getter_to_method_test.dart
index fc2abaa..fe8738b 100644
--- a/pkg/analysis_server/test/services/refactoring/convert_getter_to_method_test.dart
+++ b/pkg/analysis_server/test/services/refactoring/convert_getter_to_method_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/services/refactoring/refactoring.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart' hide ElementKind;
diff --git a/pkg/analysis_server/test/services/refactoring/convert_method_to_getter_test.dart b/pkg/analysis_server/test/services/refactoring/convert_method_to_getter_test.dart
index c7a468d..7195696 100644
--- a/pkg/analysis_server/test/services/refactoring/convert_method_to_getter_test.dart
+++ b/pkg/analysis_server/test/services/refactoring/convert_method_to_getter_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/services/refactoring/refactoring.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/src/generated/testing/element_search.dart';
diff --git a/pkg/analysis_server/test/services/refactoring/extract_local_test.dart b/pkg/analysis_server/test/services/refactoring/extract_local_test.dart
index 5d89491..4ffad65 100644
--- a/pkg/analysis_server/test/services/refactoring/extract_local_test.dart
+++ b/pkg/analysis_server/test/services/refactoring/extract_local_test.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:convert';
 
 import 'package:analysis_server/src/services/linter/lint_names.dart';
diff --git a/pkg/analysis_server/test/services/refactoring/extract_method_test.dart b/pkg/analysis_server/test/services/refactoring/extract_method_test.dart
index bee3353..5f53c00 100644
--- a/pkg/analysis_server/test/services/refactoring/extract_method_test.dart
+++ b/pkg/analysis_server/test/services/refactoring/extract_method_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/services/refactoring/extract_method.dart';
 import 'package:analysis_server/src/services/refactoring/refactoring.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
diff --git a/pkg/analysis_server/test/services/refactoring/extract_widget_test.dart b/pkg/analysis_server/test/services/refactoring/extract_widget_test.dart
index 9f2dd3a..b25f74c 100644
--- a/pkg/analysis_server/test/services/refactoring/extract_widget_test.dart
+++ b/pkg/analysis_server/test/services/refactoring/extract_widget_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/services/refactoring/extract_widget.dart';
 import 'package:analysis_server/src/services/refactoring/refactoring.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
diff --git a/pkg/analysis_server/test/services/refactoring/inline_method_test.dart b/pkg/analysis_server/test/services/refactoring/inline_method_test.dart
index 1fa40a3..04f61a5 100644
--- a/pkg/analysis_server/test/services/refactoring/inline_method_test.dart
+++ b/pkg/analysis_server/test/services/refactoring/inline_method_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/services/refactoring/inline_method.dart';
 import 'package:analysis_server/src/services/refactoring/refactoring.dart';
 import 'package:analyzer/src/generated/source.dart';
diff --git a/pkg/analysis_server/test/services/refactoring/move_file_test.dart b/pkg/analysis_server/test/services/refactoring/move_file_test.dart
index d9a993f..6fdbfda 100644
--- a/pkg/analysis_server/test/services/refactoring/move_file_test.dart
+++ b/pkg/analysis_server/test/services/refactoring/move_file_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/protocol_server.dart';
 import 'package:analysis_server/src/services/refactoring/refactoring.dart';
 import 'package:test/test.dart';
diff --git a/pkg/analysis_server/test/services/search/hierarchy_test.dart b/pkg/analysis_server/test/services/search/hierarchy_test.dart
index 8aba26f..b74fc20 100644
--- a/pkg/analysis_server/test/services/search/hierarchy_test.dart
+++ b/pkg/analysis_server/test/services/search/hierarchy_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/services/search/hierarchy.dart';
 import 'package:analysis_server/src/services/search/search_engine_internal.dart';
 import 'package:analyzer/dart/element/element.dart';
diff --git a/pkg/analysis_server/test/services/search/search_engine_test.dart b/pkg/analysis_server/test/services/search/search_engine_test.dart
index b88c020..9c46788 100644
--- a/pkg/analysis_server/test/services/search/search_engine_test.dart
+++ b/pkg/analysis_server/test/services/search/search_engine_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/services/search/search_engine.dart';
 import 'package:analysis_server/src/services/search/search_engine_internal.dart';
 import 'package:analyzer/dart/element/element.dart';
diff --git a/pkg/analysis_server/test/socket_server_test.dart b/pkg/analysis_server/test/socket_server_test.dart
index c546b23..d62ab2e 100644
--- a/pkg/analysis_server/test/socket_server_test.dart
+++ b/pkg/analysis_server/test/socket_server_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol.dart';
 import 'package:analysis_server/protocol/protocol_constants.dart';
 import 'package:analysis_server/protocol/protocol_generated.dart';
diff --git a/pkg/analysis_server/test/src/computer/closing_labels_computer_test.dart b/pkg/analysis_server/test/src/computer/closing_labels_computer_test.dart
index ba1761d..85369d1 100644
--- a/pkg/analysis_server/test/src/computer/closing_labels_computer_test.dart
+++ b/pkg/analysis_server/test/src/computer/closing_labels_computer_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analysis_server/src/computer/computer_closingLabels.dart';
 import 'package:test/test.dart';
diff --git a/pkg/analysis_server/test/src/computer/folding_computer_test.dart b/pkg/analysis_server/test/src/computer/folding_computer_test.dart
index 935dd8d..0f3fa04 100644
--- a/pkg/analysis_server/test/src/computer/folding_computer_test.dart
+++ b/pkg/analysis_server/test/src/computer/folding_computer_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/computer/computer_folding.dart';
 import 'package:analysis_server/src/protocol_server.dart';
 import 'package:test/test.dart';
diff --git a/pkg/analysis_server/test/src/computer/highlights2_computer_test.dart b/pkg/analysis_server/test/src/computer/highlights2_computer_test.dart
index 5f3e70a0..33aa117 100644
--- a/pkg/analysis_server/test/src/computer/highlights2_computer_test.dart
+++ b/pkg/analysis_server/test/src/computer/highlights2_computer_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/computer/computer_highlights2.dart';
 import 'package:analysis_server/src/protocol_server.dart';
 import 'package:test/test.dart';
diff --git a/pkg/analysis_server/test/src/computer/highlights_computer_test.dart b/pkg/analysis_server/test/src/computer/highlights_computer_test.dart
index 854a638..b9d1af4 100644
--- a/pkg/analysis_server/test/src/computer/highlights_computer_test.dart
+++ b/pkg/analysis_server/test/src/computer/highlights_computer_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/computer/computer_highlights.dart';
 import 'package:analysis_server/src/protocol_server.dart';
 import 'package:test/test.dart';
diff --git a/pkg/analysis_server/test/src/computer/import_elements_computer_test.dart b/pkg/analysis_server/test/src/computer/import_elements_computer_test.dart
index fd511a0..af893d6 100644
--- a/pkg/analysis_server/test/src/computer/import_elements_computer_test.dart
+++ b/pkg/analysis_server/test/src/computer/import_elements_computer_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analysis_server/src/computer/import_elements_computer.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
diff --git a/pkg/analysis_server/test/src/computer/imported_elements_computer_test.dart b/pkg/analysis_server/test/src/computer/imported_elements_computer_test.dart
index c4a6a06..a00364a 100644
--- a/pkg/analysis_server/test/src/computer/imported_elements_computer_test.dart
+++ b/pkg/analysis_server/test/src/computer/imported_elements_computer_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analysis_server/src/computer/imported_elements_computer.dart';
 import 'package:test/test.dart';
diff --git a/pkg/analysis_server/test/src/computer/outline_computer_test.dart b/pkg/analysis_server/test/src/computer/outline_computer_test.dart
index 48985ee..9f38295 100644
--- a/pkg/analysis_server/test/src/computer/outline_computer_test.dart
+++ b/pkg/analysis_server/test/src/computer/outline_computer_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/computer/computer_outline.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
 import 'package:meta/meta.dart';
diff --git a/pkg/analysis_server/test/src/domain_abstract_test.dart b/pkg/analysis_server/test/src/domain_abstract_test.dart
index d21ce87..eb1fdb9 100644
--- a/pkg/analysis_server/test/src/domain_abstract_test.dart
+++ b/pkg/analysis_server/test/src/domain_abstract_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/domain_abstract.dart';
 import 'package:analysis_server/src/plugin/plugin_manager.dart';
 import 'package:analysis_server/src/protocol_server.dart' hide Element;
diff --git a/pkg/analysis_server/test/src/domains/completion/available_suggestions_base.dart b/pkg/analysis_server/test/src/domains/completion/available_suggestions_base.dart
index 469ba02..3fac860 100644
--- a/pkg/analysis_server/test/src/domains/completion/available_suggestions_base.dart
+++ b/pkg/analysis_server/test/src/domains/completion/available_suggestions_base.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:convert';
 
 import 'package:analysis_server/protocol/protocol.dart';
diff --git a/pkg/analysis_server/test/src/domains/completion/get_suggestion_details_test.dart b/pkg/analysis_server/test/src/domains/completion/get_suggestion_details_test.dart
index f0bed0b..156c4b4 100644
--- a/pkg/analysis_server/test/src/domains/completion/get_suggestion_details_test.dart
+++ b/pkg/analysis_server/test/src/domains/completion/get_suggestion_details_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analysis_server/src/protocol_server.dart';
 import 'package:meta/meta.dart';
diff --git a/pkg/analysis_server/test/src/domains/execution/completion_test.dart b/pkg/analysis_server/test/src/domains/execution/completion_test.dart
index 6dda0c3..5e7d02c 100644
--- a/pkg/analysis_server/test/src/domains/execution/completion_test.dart
+++ b/pkg/analysis_server/test/src/domains/execution/completion_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/domains/execution/completion.dart';
 import 'package:analysis_server/src/protocol_server.dart';
 import 'package:test/test.dart';
diff --git a/pkg/analysis_server/test/src/flutter/flutter_outline_computer_test.dart b/pkg/analysis_server/test/src/flutter/flutter_outline_computer_test.dart
index 58c910f..02fff3b 100644
--- a/pkg/analysis_server/test/src/flutter/flutter_outline_computer_test.dart
+++ b/pkg/analysis_server/test/src/flutter/flutter_outline_computer_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/flutter/flutter_outline_computer.dart';
 import 'package:analysis_server/src/protocol_server.dart';
 import 'package:analyzer/dart/analysis/results.dart';
diff --git a/pkg/analysis_server/test/src/plugin/plugin_manager_test.dart b/pkg/analysis_server/test/src/plugin/plugin_manager_test.dart
index 72653d2..ba21d9d 100644
--- a/pkg/analysis_server/test/src/plugin/plugin_manager_test.dart
+++ b/pkg/analysis_server/test/src/plugin/plugin_manager_test.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:io' as io;
 
 import 'package:analysis_server/src/plugin/notification_manager.dart';
diff --git a/pkg/analysis_server/test/src/services/correction/assist/assist_processor.dart b/pkg/analysis_server/test/src/services/correction/assist/assist_processor.dart
index 072f7bc..3a9e20f 100644
--- a/pkg/analysis_server/test/src/services/correction/assist/assist_processor.dart
+++ b/pkg/analysis_server/test/src/services/correction/assist/assist_processor.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/plugin/edit/assist/assist_core.dart';
 import 'package:analysis_server/src/services/correction/assist.dart';
 import 'package:analysis_server/src/services/correction/assist_internal.dart';
diff --git a/pkg/analysis_server/test/src/services/correction/fix/bulk/bulk_fix_processor.dart b/pkg/analysis_server/test/src/services/correction/fix/bulk/bulk_fix_processor.dart
index 6ef1c95..ef3a83a 100644
--- a/pkg/analysis_server/test/src/services/correction/fix/bulk/bulk_fix_processor.dart
+++ b/pkg/analysis_server/test/src/services/correction/fix/bulk/bulk_fix_processor.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/services/correction/bulk_fix_processor.dart';
 import 'package:analysis_server/src/services/correction/change_workspace.dart';
 import 'package:analyzer/src/dart/analysis/byte_store.dart';
diff --git a/pkg/analysis_server/test/src/services/correction/fix/fix_processor.dart b/pkg/analysis_server/test/src/services/correction/fix/fix_processor.dart
index 4808f8b..f5d7d59 100644
--- a/pkg/analysis_server/test/src/services/correction/fix/fix_processor.dart
+++ b/pkg/analysis_server/test/src/services/correction/fix/fix_processor.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/plugin/edit/fix/fix_core.dart';
 import 'package:analysis_server/src/services/correction/change_workspace.dart';
 import 'package:analysis_server/src/services/correction/fix.dart';
diff --git a/pkg/analysis_server/test/stress/completion/completion_runner.dart b/pkg/analysis_server/test/stress/completion/completion_runner.dart
index 51c2445..3f69cff 100644
--- a/pkg/analysis_server/test/stress/completion/completion_runner.dart
+++ b/pkg/analysis_server/test/stress/completion/completion_runner.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server/src/services/completion/completion_core.dart';
 import 'package:analysis_server/src/services/completion/completion_performance.dart';
 import 'package:analysis_server/src/services/completion/dart/completion_manager.dart';
diff --git a/pkg/analysis_server/test/stress/replay/replay.dart b/pkg/analysis_server/test/stress/replay/replay.dart
index f453567..64c5ea0 100644
--- a/pkg/analysis_server/test/stress/replay/replay.dart
+++ b/pkg/analysis_server/test/stress/replay/replay.dart
@@ -3,7 +3,6 @@
 // BSD-style license that can be found in the LICENSE file.
 
 /// A stress test for the analysis server.
-import 'dart:async';
 import 'dart:io';
 import 'dart:math' as math;
 
diff --git a/pkg/analysis_server/tool/completion_metrics/code_metrics.dart b/pkg/analysis_server/tool/completion_metrics/code_metrics.dart
index fec950b..1ae1151 100644
--- a/pkg/analysis_server/tool/completion_metrics/code_metrics.dart
+++ b/pkg/analysis_server/tool/completion_metrics/code_metrics.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:io' as io;
 
 import 'package:analyzer/dart/analysis/analysis_context_collection.dart';
diff --git a/pkg/analysis_server/tool/completion_metrics/completion_metrics.dart b/pkg/analysis_server/tool/completion_metrics/completion_metrics.dart
index 3e57965..309d8a1 100644
--- a/pkg/analysis_server/tool/completion_metrics/completion_metrics.dart
+++ b/pkg/analysis_server/tool/completion_metrics/completion_metrics.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:convert';
 import 'dart:io' as io;
 import 'dart:math' as math;
diff --git a/pkg/analysis_server/tool/completion_metrics/flutter_metrics.dart b/pkg/analysis_server/tool/completion_metrics/flutter_metrics.dart
index 817a3e8..8ff6195 100644
--- a/pkg/analysis_server/tool/completion_metrics/flutter_metrics.dart
+++ b/pkg/analysis_server/tool/completion_metrics/flutter_metrics.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:io' as io;
 
 import 'package:analysis_server/src/utilities/flutter.dart';
diff --git a/pkg/analysis_server/tool/completion_metrics/implicit_type_declarations.dart b/pkg/analysis_server/tool/completion_metrics/implicit_type_declarations.dart
index 2c51ca3..4b9b1c0 100644
--- a/pkg/analysis_server/tool/completion_metrics/implicit_type_declarations.dart
+++ b/pkg/analysis_server/tool/completion_metrics/implicit_type_declarations.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:io' as io;
 
 import 'package:analysis_server/src/status/pages.dart';
diff --git a/pkg/analysis_server/tool/completion_metrics/relevance_metrics.dart b/pkg/analysis_server/tool/completion_metrics/relevance_metrics.dart
index d1da6d3..e043511 100644
--- a/pkg/analysis_server/tool/completion_metrics/relevance_metrics.dart
+++ b/pkg/analysis_server/tool/completion_metrics/relevance_metrics.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:io' as io;
 import 'dart:math' as math;
 
diff --git a/pkg/analysis_server/tool/completion_metrics/relevance_table_generator.dart b/pkg/analysis_server/tool/completion_metrics/relevance_table_generator.dart
index dacc489..846e22d 100644
--- a/pkg/analysis_server/tool/completion_metrics/relevance_table_generator.dart
+++ b/pkg/analysis_server/tool/completion_metrics/relevance_table_generator.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:io' as io;
 
 import 'package:_fe_analyzer_shared/src/base/syntactic_entity.dart';
diff --git a/pkg/analysis_server/tool/instrumentation/server.dart b/pkg/analysis_server/tool/instrumentation/server.dart
index 70f3caf..150eb9e 100644
--- a/pkg/analysis_server/tool/instrumentation/server.dart
+++ b/pkg/analysis_server/tool/instrumentation/server.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:collection';
 import 'dart:io';
 
diff --git a/pkg/analysis_server/tool/lsp_spec/generate_all.dart b/pkg/analysis_server/tool/lsp_spec/generate_all.dart
index 2f29b7f..26b8916 100644
--- a/pkg/analysis_server/tool/lsp_spec/generate_all.dart
+++ b/pkg/analysis_server/tool/lsp_spec/generate_all.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:io';
 
 import 'package:analysis_server/src/utilities/strings.dart';
diff --git a/pkg/analyzer/lib/dart/analysis/session.dart b/pkg/analyzer/lib/dart/analysis/session.dart
index a4db043..276b81e 100644
--- a/pkg/analyzer/lib/dart/analysis/session.dart
+++ b/pkg/analyzer/lib/dart/analysis/session.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/dart/analysis/analysis_context.dart';
 import 'package:analyzer/dart/analysis/declared_variables.dart';
 import 'package:analyzer/dart/analysis/results.dart';
diff --git a/pkg/analyzer/lib/dart/analysis/utilities.dart b/pkg/analyzer/lib/dart/analysis/utilities.dart
index 2082d97..10fb211 100644
--- a/pkg/analyzer/lib/dart/analysis/utilities.dart
+++ b/pkg/analyzer/lib/dart/analysis/utilities.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/dart/analysis/analysis_context.dart';
 import 'package:analyzer/dart/analysis/analysis_context_collection.dart';
 import 'package:analyzer/dart/analysis/features.dart';
diff --git a/pkg/analyzer/lib/file_system/file_system.dart b/pkg/analyzer/lib/file_system/file_system.dart
index c4dd4c2..ac8456c 100644
--- a/pkg/analyzer/lib/file_system/file_system.dart
+++ b/pkg/analyzer/lib/file_system/file_system.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/src/generated/source.dart';
 import 'package:path/path.dart';
 import 'package:watcher/watcher.dart';
diff --git a/pkg/analyzer/lib/file_system/overlay_file_system.dart b/pkg/analyzer/lib/file_system/overlay_file_system.dart
index af97ba7..35dde56 100644
--- a/pkg/analyzer/lib/file_system/overlay_file_system.dart
+++ b/pkg/analyzer/lib/file_system/overlay_file_system.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:convert';
 import 'dart:core';
 import 'dart:typed_data';
diff --git a/pkg/analyzer/lib/file_system/physical_file_system.dart b/pkg/analyzer/lib/file_system/physical_file_system.dart
index f335f05..0f0ee0d 100644
--- a/pkg/analyzer/lib/file_system/physical_file_system.dart
+++ b/pkg/analyzer/lib/file_system/physical_file_system.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:io' as io;
 import 'dart:typed_data';
 
diff --git a/pkg/analyzer/lib/instrumentation/file_instrumentation.dart b/pkg/analyzer/lib/instrumentation/file_instrumentation.dart
index 47d50e6..7985cd2 100644
--- a/pkg/analyzer/lib/instrumentation/file_instrumentation.dart
+++ b/pkg/analyzer/lib/instrumentation/file_instrumentation.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:io';
 
 import 'package:analyzer/instrumentation/instrumentation.dart';
diff --git a/pkg/analyzer/lib/src/dart/analysis/file_byte_store.dart b/pkg/analyzer/lib/src/dart/analysis/file_byte_store.dart
index 2b3d215..506fb2a 100644
--- a/pkg/analyzer/lib/src/dart/analysis/file_byte_store.dart
+++ b/pkg/analyzer/lib/src/dart/analysis/file_byte_store.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:io';
 import 'dart:isolate';
 import 'dart:typed_data';
diff --git a/pkg/analyzer/lib/src/dart/analysis/performance_logger.dart b/pkg/analyzer/lib/src/dart/analysis/performance_logger.dart
index 4f25fe1..245f058 100644
--- a/pkg/analyzer/lib/src/dart/analysis/performance_logger.dart
+++ b/pkg/analyzer/lib/src/dart/analysis/performance_logger.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 /// This class is used to gather and print performance information.
 class PerformanceLog {
   final StringSink sink;
diff --git a/pkg/analyzer/lib/src/dart/analysis/search.dart b/pkg/analyzer/lib/src/dart/analysis/search.dart
index 028e54c..31236b3 100644
--- a/pkg/analyzer/lib/src/dart/analysis/search.dart
+++ b/pkg/analyzer/lib/src/dart/analysis/search.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/dart/analysis/results.dart';
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
diff --git a/pkg/analyzer/lib/src/dart/analysis/session.dart b/pkg/analyzer/lib/src/dart/analysis/session.dart
index 78df548..4bfedf3 100644
--- a/pkg/analyzer/lib/src/dart/analysis/session.dart
+++ b/pkg/analyzer/lib/src/dart/analysis/session.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/dart/analysis/analysis_context.dart';
 import 'package:analyzer/dart/analysis/declared_variables.dart';
 import 'package:analyzer/dart/analysis/results.dart';
diff --git a/pkg/analyzer/lib/src/dart/analysis/session_helper.dart b/pkg/analyzer/lib/src/dart/analysis/session_helper.dart
index 87ec58a..a7d78a6 100644
--- a/pkg/analyzer/lib/src/dart/analysis/session_helper.dart
+++ b/pkg/analyzer/lib/src/dart/analysis/session_helper.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/dart/analysis/results.dart';
 import 'package:analyzer/dart/analysis/session.dart';
 import 'package:analyzer/dart/element/element.dart';
diff --git a/pkg/analyzer/lib/src/dart/resolver/assignment_expression_resolver.dart b/pkg/analyzer/lib/src/dart/resolver/assignment_expression_resolver.dart
index 274b4be..3cf8743 100644
--- a/pkg/analyzer/lib/src/dart/resolver/assignment_expression_resolver.dart
+++ b/pkg/analyzer/lib/src/dart/resolver/assignment_expression_resolver.dart
@@ -265,9 +265,9 @@
           CompileTimeErrorCode.ASSIGNMENT_TO_CONST,
           left,
         );
-      } else if (variable.isFinal && !variable.isLate) {
+      } else if (variable.setter == null) {
         if (variable is FieldElement) {
-          if (variable.setter == null && variable.isSynthetic) {
+          if (variable.isSynthetic) {
             _errorReporter.reportErrorForNode(
               CompileTimeErrorCode.ASSIGNMENT_TO_FINAL_NO_SETTER,
               left,
diff --git a/pkg/analyzer/lib/src/generated/error_verifier.dart b/pkg/analyzer/lib/src/generated/error_verifier.dart
index ef6c8c9..81b0968 100644
--- a/pkg/analyzer/lib/src/generated/error_verifier.dart
+++ b/pkg/analyzer/lib/src/generated/error_verifier.dart
@@ -1647,39 +1647,53 @@
       highlightedNode = expression.propertyName;
     }
     // check if element is assignable
-    Element toVariable(Element element) {
-      return element is PropertyAccessorElement ? element.variable : element;
-    }
-
-    element = toVariable(element);
     if (element is VariableElement) {
       if (element.isConst) {
         _errorReporter.reportErrorForNode(
-            CompileTimeErrorCode.ASSIGNMENT_TO_CONST, expression);
-      } else if (element.isFinal && !element.isLate) {
-        if (element is FieldElementImpl) {
-          if (element.setter == null && element.isSynthetic) {
-            _errorReporter.reportErrorForNode(
-                CompileTimeErrorCode.ASSIGNMENT_TO_FINAL_NO_SETTER,
-                highlightedNode,
-                [element.name, element.enclosingElement.displayName]);
-          } else {
-            _errorReporter.reportErrorForNode(
-                CompileTimeErrorCode.ASSIGNMENT_TO_FINAL,
-                highlightedNode,
-                [element.name]);
-          }
-          return;
-        }
-        if (_isNonNullableByDefault && element is PromotableElement) {
+          CompileTimeErrorCode.ASSIGNMENT_TO_CONST,
+          expression,
+        );
+      } else if (element.isFinal) {
+        if (_isNonNullableByDefault) {
           // Handled during resolution, with flow analysis.
         } else {
           _errorReporter.reportErrorForNode(
-              CompileTimeErrorCode.ASSIGNMENT_TO_FINAL_LOCAL,
-              highlightedNode,
-              [element.name]);
+            CompileTimeErrorCode.ASSIGNMENT_TO_FINAL_LOCAL,
+            expression,
+            [element.name],
+          );
         }
       }
+    } else if (element is PropertyAccessorElement && element.isGetter) {
+      var variable = element.variable;
+      if (variable.isConst) {
+        _errorReporter.reportErrorForNode(
+          CompileTimeErrorCode.ASSIGNMENT_TO_CONST,
+          expression,
+        );
+      } else if (variable.setter == null) {
+        if (variable is FieldElement) {
+          if (variable.isSynthetic) {
+            _errorReporter.reportErrorForNode(
+              CompileTimeErrorCode.ASSIGNMENT_TO_FINAL_NO_SETTER,
+              highlightedNode,
+              [variable.name, variable.enclosingElement.displayName],
+            );
+          } else {
+            _errorReporter.reportErrorForNode(
+              CompileTimeErrorCode.ASSIGNMENT_TO_FINAL,
+              highlightedNode,
+              [variable.name],
+            );
+          }
+          return;
+        }
+        _errorReporter.reportErrorForNode(
+          CompileTimeErrorCode.ASSIGNMENT_TO_FINAL_LOCAL,
+          highlightedNode,
+          [variable.name],
+        );
+      }
     } else if (element is FunctionElement) {
       _errorReporter.reportErrorForNode(
           CompileTimeErrorCode.ASSIGNMENT_TO_FUNCTION, expression);
diff --git a/pkg/analyzer/lib/src/lint/analysis.dart b/pkg/analyzer/lib/src/lint/analysis.dart
index 2990f6d..5777705 100644
--- a/pkg/analyzer/lib/src/lint/analysis.dart
+++ b/pkg/analyzer/lib/src/lint/analysis.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:collection';
 import 'dart:io' as io;
 
diff --git a/pkg/analyzer/lib/src/lint/linter.dart b/pkg/analyzer/lib/src/lint/linter.dart
index 4261e0c..edabdfa 100644
--- a/pkg/analyzer/lib/src/lint/linter.dart
+++ b/pkg/analyzer/lib/src/lint/linter.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:io';
 
 import 'package:analyzer/dart/analysis/declared_variables.dart';
diff --git a/pkg/analyzer/lib/src/lint/project.dart b/pkg/analyzer/lib/src/lint/project.dart
index 7498abb..18a944b 100644
--- a/pkg/analyzer/lib/src/lint/project.dart
+++ b/pkg/analyzer/lib/src/lint/project.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:io';
 
 import 'package:analyzer/dart/analysis/results.dart';
diff --git a/pkg/analyzer/test/file_system/memory_file_system_test.dart b/pkg/analyzer/test/file_system/memory_file_system_test.dart
index 8b509ce..00d30bc 100644
--- a/pkg/analyzer/test/file_system/memory_file_system_test.dart
+++ b/pkg/analyzer/test/file_system/memory_file_system_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/file_system/memory_file_system.dart';
 import 'package:analyzer/src/generated/engine.dart' show TimestampedData;
diff --git a/pkg/analyzer/test/file_system/physical_resource_provider_watch_test.dart b/pkg/analyzer/test/file_system/physical_resource_provider_watch_test.dart
index 5dabf51..71ab2b6 100644
--- a/pkg/analyzer/test/file_system/physical_resource_provider_watch_test.dart
+++ b/pkg/analyzer/test/file_system/physical_resource_provider_watch_test.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:io' as io;
 
 import 'package:analyzer/file_system/file_system.dart';
diff --git a/pkg/analyzer/test/generated/element_resolver_test.dart b/pkg/analyzer/test/generated/element_resolver_test.dart
index a88deb2..f9ae380 100644
--- a/pkg/analyzer/test/generated/element_resolver_test.dart
+++ b/pkg/analyzer/test/generated/element_resolver_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/dart/analysis/features.dart';
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/standard_ast_factory.dart';
diff --git a/pkg/analyzer/test/generated/invalid_code_test.dart b/pkg/analyzer/test/generated/invalid_code_test.dart
index dc3b656..5f397fd 100644
--- a/pkg/analyzer/test/generated/invalid_code_test.dart
+++ b/pkg/analyzer/test/generated/invalid_code_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/dart/element/nullability_suffix.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
diff --git a/pkg/analyzer/test/generated/non_error_resolver_test.dart b/pkg/analyzer/test/generated/non_error_resolver_test.dart
index ac6d07b..c616675 100644
--- a/pkg/analyzer/test/generated/non_error_resolver_test.dart
+++ b/pkg/analyzer/test/generated/non_error_resolver_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/src/error/codes.dart';
@@ -127,7 +125,6 @@
 }
 ''');
     await assertNoErrorsInCode(r'''
-import 'dart:async';
 import 'lib.dart';
 main() {
   print(Future.zero);
@@ -291,7 +288,6 @@
 
   test_assert_with_message_await() async {
     await assertNoErrorsInCode('''
-import 'dart:async';
 f() async {
   assert(false, await g());
 }
diff --git a/pkg/analyzer/test/generated/strong_mode_test.dart b/pkg/analyzer/test/generated/strong_mode_test.dart
index 8e58c95..e46eb3b 100644
--- a/pkg/analyzer/test/generated/strong_mode_test.dart
+++ b/pkg/analyzer/test/generated/strong_mode_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/nullability_suffix.dart';
diff --git a/pkg/analyzer/test/resource_utils.dart b/pkg/analyzer/test/resource_utils.dart
index f991767..c38b139 100644
--- a/pkg/analyzer/test/resource_utils.dart
+++ b/pkg/analyzer/test/resource_utils.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:core';
 
 import 'package:analyzer/file_system/file_system.dart';
diff --git a/pkg/analyzer/test/src/dart/analysis/driver_test.dart b/pkg/analyzer/test/src/dart/analysis/driver_test.dart
index 493d29a..0743fd3 100644
--- a/pkg/analyzer/test/src/dart/analysis/driver_test.dart
+++ b/pkg/analyzer/test/src/dart/analysis/driver_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/dart/analysis/results.dart';
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
diff --git a/pkg/analyzer/test/src/dart/analysis/index_test.dart b/pkg/analyzer/test/src/dart/analysis/index_test.dart
index 6f31683..d7c8abd 100644
--- a/pkg/analyzer/test/src/dart/analysis/index_test.dart
+++ b/pkg/analyzer/test/src/dart/analysis/index_test.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:convert';
 
 import 'package:analyzer/dart/analysis/results.dart';
diff --git a/pkg/analyzer/test/src/dart/analysis/mutex_test.dart b/pkg/analyzer/test/src/dart/analysis/mutex_test.dart
index 5ffbda9..5d675d7 100644
--- a/pkg/analyzer/test/src/dart/analysis/mutex_test.dart
+++ b/pkg/analyzer/test/src/dart/analysis/mutex_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/src/dart/analysis/mutex.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
diff --git a/pkg/analyzer/test/src/dart/analysis/search_test.dart b/pkg/analyzer/test/src/dart/analysis/search_test.dart
index 37af8b4..c3174e4 100644
--- a/pkg/analyzer/test/src/dart/analysis/search_test.dart
+++ b/pkg/analyzer/test/src/dart/analysis/search_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/dart/analysis/features.dart';
 import 'package:analyzer/dart/analysis/results.dart';
 import 'package:analyzer/dart/ast/ast.dart' hide Declaration;
diff --git a/pkg/analyzer/test/src/dart/resolution/context_collection_resolution.dart b/pkg/analyzer/test/src/dart/resolution/context_collection_resolution.dart
index c1d5dd2..4e85656 100644
--- a/pkg/analyzer/test/src/dart/resolution/context_collection_resolution.dart
+++ b/pkg/analyzer/test/src/dart/resolution/context_collection_resolution.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/dart/analysis/analysis_context.dart';
 import 'package:analyzer/dart/analysis/analysis_context_collection.dart';
 import 'package:analyzer/dart/analysis/results.dart';
diff --git a/pkg/analyzer/test/src/dart/resolution/resolution.dart b/pkg/analyzer/test/src/dart/resolution/resolution.dart
index 1368e36..cb4d4f8 100644
--- a/pkg/analyzer/test/src/dart/resolution/resolution.dart
+++ b/pkg/analyzer/test/src/dart/resolution/resolution.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/dart/analysis/results.dart';
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
diff --git a/pkg/analyzer/test/src/diagnostics/assignment_to_final_local_test.dart b/pkg/analyzer/test/src/diagnostics/assignment_to_final_local_test.dart
index 35822d2..bd8e7d6 100644
--- a/pkg/analyzer/test/src/diagnostics/assignment_to_final_local_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/assignment_to_final_local_test.dart
@@ -160,13 +160,15 @@
   }
 
   test_topLevelVariable_late() async {
-    await assertNoErrorsInCode('''
+    await assertErrorsInCode('''
 late final int a;
 late final int b = 0;
 void f() {
   a = 1;
   b = 1;
 }
-''');
+''', [
+      error(CompileTimeErrorCode.ASSIGNMENT_TO_FINAL_LOCAL, 62, 1),
+    ]);
   }
 }
diff --git a/pkg/analyzer/test/src/diagnostics/assignment_to_final_test.dart b/pkg/analyzer/test/src/diagnostics/assignment_to_final_test.dart
index ddf030f..bc8888d 100644
--- a/pkg/analyzer/test/src/diagnostics/assignment_to_final_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/assignment_to_final_test.dart
@@ -46,8 +46,23 @@
 @reflectiveTest
 class AssignmentToFinalWithNullSafetyTest extends AssignmentToFinalTest
     with WithNullSafetyMixin {
-  test_field_late() async {
-    await assertNoErrorsInCode('''
+  test_field_late_propertyAccess() async {
+    await assertErrorsInCode('''
+class A {
+  late final int a;
+  late final int b = 0;
+  void m() {
+    this.a = 1;
+    this.b = 1;
+  }
+}
+''', [
+      error(CompileTimeErrorCode.ASSIGNMENT_TO_FINAL, 92, 1),
+    ]);
+  }
+
+  test_field_late_simpleIdentifier() async {
+    await assertErrorsInCode('''
 class A {
   late final int a;
   late final int b = 0;
@@ -56,11 +71,29 @@
     b = 1;
   }
 }
-''');
+''', [
+      error(CompileTimeErrorCode.ASSIGNMENT_TO_FINAL, 82, 1),
+    ]);
   }
 
-  test_field_static_late() async {
-    await assertNoErrorsInCode('''
+  test_field_static_final_late_prefixedIdentifier() async {
+    await assertErrorsInCode('''
+class A {
+  static late final int a;
+  static late final int b = 0;
+}
+
+void f() {
+  A.a = 1;
+  A.b = 1;
+}
+''', [
+      error(CompileTimeErrorCode.ASSIGNMENT_TO_FINAL, 97, 1),
+    ]);
+  }
+
+  test_field_static_final_late_simpleIdentifier() async {
+    await assertErrorsInCode('''
 class A {
   static late final int a;
   static late final int b = 0;
@@ -69,7 +102,9 @@
     b = 1;
   }
 }
-''');
+''', [
+      error(CompileTimeErrorCode.ASSIGNMENT_TO_FINAL, 96, 1),
+    ]);
   }
 
   test_set_abstract_field_final_invalid() async {
diff --git a/pkg/analyzer/test/src/lint/linter/linter_context_impl_test.dart b/pkg/analyzer/test/src/lint/linter/linter_context_impl_test.dart
index 194fe57..003906c 100644
--- a/pkg/analyzer/test/src/lint/linter/linter_context_impl_test.dart
+++ b/pkg/analyzer/test/src/lint/linter/linter_context_impl_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/src/context/builder.dart';
 import 'package:analyzer/src/dart/element/inheritance_manager3.dart';
 import 'package:analyzer/src/lint/linter.dart';
diff --git a/pkg/analyzer/test/src/lint/linter/resolve_name_in_scope_test.dart b/pkg/analyzer/test/src/lint/linter/resolve_name_in_scope_test.dart
index 8ad3449..036ee36 100644
--- a/pkg/analyzer/test/src/lint/linter/resolve_name_in_scope_test.dart
+++ b/pkg/analyzer/test/src/lint/linter/resolve_name_in_scope_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/src/error/codes.dart';
diff --git a/pkg/analyzer/test/src/summary/resynthesize_common.dart b/pkg/analyzer/test/src/summary/resynthesize_common.dart
index 80b832c..2a30b09 100644
--- a/pkg/analyzer/test/src/summary/resynthesize_common.dart
+++ b/pkg/analyzer/test/src/summary/resynthesize_common.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/dart/analysis/declared_variables.dart';
 import 'package:analyzer/dart/analysis/features.dart';
 import 'package:analyzer/dart/ast/ast.dart';
diff --git a/pkg/analyzer/test/src/summary/top_level_inference_test.dart b/pkg/analyzer/test/src/summary/top_level_inference_test.dart
index 1d3f695..96d5cac 100644
--- a/pkg/analyzer/test/src/summary/top_level_inference_test.dart
+++ b/pkg/analyzer/test/src/summary/top_level_inference_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/dart/analysis/results.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/src/dart/analysis/experiments.dart';
diff --git a/pkg/analyzer/test/src/task/strong/inferred_type_test.dart b/pkg/analyzer/test/src/task/strong/inferred_type_test.dart
index 3484cc7..6c8f375 100644
--- a/pkg/analyzer/test/src/task/strong/inferred_type_test.dart
+++ b/pkg/analyzer/test/src/task/strong/inferred_type_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
diff --git a/pkg/analyzer_cli/lib/src/analyzer_impl.dart b/pkg/analyzer_cli/lib/src/analyzer_impl.dart
index 2f6c5ae..4294f1c 100644
--- a/pkg/analyzer_cli/lib/src/analyzer_impl.dart
+++ b/pkg/analyzer_cli/lib/src/analyzer_impl.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:io';
 
 import 'package:analyzer/dart/analysis/results.dart';
diff --git a/pkg/analyzer_cli/lib/src/batch_mode.dart b/pkg/analyzer_cli/lib/src/batch_mode.dart
index 3a34b88..995af86 100644
--- a/pkg/analyzer_cli/lib/src/batch_mode.dart
+++ b/pkg/analyzer_cli/lib/src/batch_mode.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:convert';
 import 'dart:io' show exitCode, stdin;
 
diff --git a/pkg/analyzer_cli/lib/src/build_mode.dart b/pkg/analyzer_cli/lib/src/build_mode.dart
index 7bdcc3b..df41c5e 100644
--- a/pkg/analyzer_cli/lib/src/build_mode.dart
+++ b/pkg/analyzer_cli/lib/src/build_mode.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:io' as io;
 import 'dart:isolate';
 
diff --git a/pkg/analyzer_cli/lib/src/driver.dart b/pkg/analyzer_cli/lib/src/driver.dart
index ead05a3..832785a 100644
--- a/pkg/analyzer_cli/lib/src/driver.dart
+++ b/pkg/analyzer_cli/lib/src/driver.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:io' as io;
 import 'dart:isolate';
 
diff --git a/pkg/analyzer_cli/lib/starter.dart b/pkg/analyzer_cli/lib/starter.dart
index 0475ba8..ad8e268 100644
--- a/pkg/analyzer_cli/lib/starter.dart
+++ b/pkg/analyzer_cli/lib/starter.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:isolate';
 
 import 'package:analyzer_cli/src/driver.dart';
diff --git a/pkg/analyzer_cli/test/analysis_options_test.dart b/pkg/analyzer_cli/test/analysis_options_test.dart
index b3d9a3b..d112a6e 100644
--- a/pkg/analyzer_cli/test/analysis_options_test.dart
+++ b/pkg/analyzer_cli/test/analysis_options_test.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:io';
 
 import 'package:analyzer_cli/src/driver.dart' show Driver, outSink, errorSink;
diff --git a/pkg/analyzer_cli/test/build_mode_test.dart b/pkg/analyzer_cli/test/build_mode_test.dart
index aee3830..5027e1f 100644
--- a/pkg/analyzer_cli/test/build_mode_test.dart
+++ b/pkg/analyzer_cli/test/build_mode_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/file_system/memory_file_system.dart';
 import 'package:analyzer_cli/src/build_mode.dart';
 import 'package:analyzer_cli/src/driver.dart';
diff --git a/pkg/analyzer_cli/test/driver_test.dart b/pkg/analyzer_cli/test/driver_test.dart
index cc8ae522..b19066c 100644
--- a/pkg/analyzer_cli/test/driver_test.dart
+++ b/pkg/analyzer_cli/test/driver_test.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:io';
 
 import 'package:analyzer/error/error.dart';
diff --git a/pkg/analyzer_cli/test/package_prefix_test.dart b/pkg/analyzer_cli/test/package_prefix_test.dart
index 8112b0b..fbe8aac 100644
--- a/pkg/analyzer_cli/test/package_prefix_test.dart
+++ b/pkg/analyzer_cli/test/package_prefix_test.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:io' show exitCode;
 
 import 'package:analyzer_cli/src/driver.dart' show Driver, outSink, errorSink;
diff --git a/pkg/analyzer_cli/test/utils.dart b/pkg/analyzer_cli/test/utils.dart
index a7c3640..fb32e08 100644
--- a/pkg/analyzer_cli/test/utils.dart
+++ b/pkg/analyzer_cli/test/utils.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:io';
 import 'dart:mirrors';
 
diff --git a/pkg/analyzer_cli/tool/perf.dart b/pkg/analyzer_cli/tool/perf.dart
index b23105d..bd94085 100644
--- a/pkg/analyzer_cli/tool/perf.dart
+++ b/pkg/analyzer_cli/tool/perf.dart
@@ -3,7 +3,6 @@
 // BSD-style license that can be found in the LICENSE file.
 
 /// An entrypoint used to run portions of analyzer and measure its performance.
-import 'dart:async';
 import 'dart:io' show exit;
 
 import 'package:analyzer/dart/analysis/features.dart';
diff --git a/pkg/analyzer_plugin/lib/plugin/assist_mixin.dart b/pkg/analyzer_plugin/lib/plugin/assist_mixin.dart
index b006c26..051d9d0 100644
--- a/pkg/analyzer_plugin/lib/plugin/assist_mixin.dart
+++ b/pkg/analyzer_plugin/lib/plugin/assist_mixin.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/src/dart/analysis/driver.dart';
 import 'package:analyzer_plugin/plugin/plugin.dart';
 import 'package:analyzer_plugin/protocol/protocol.dart';
diff --git a/pkg/analyzer_plugin/lib/plugin/completion_mixin.dart b/pkg/analyzer_plugin/lib/plugin/completion_mixin.dart
index b8667fd..ed39aba 100644
--- a/pkg/analyzer_plugin/lib/plugin/completion_mixin.dart
+++ b/pkg/analyzer_plugin/lib/plugin/completion_mixin.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/src/dart/analysis/driver.dart';
 import 'package:analyzer_plugin/plugin/plugin.dart';
 import 'package:analyzer_plugin/protocol/protocol.dart';
diff --git a/pkg/analyzer_plugin/lib/plugin/fix_mixin.dart b/pkg/analyzer_plugin/lib/plugin/fix_mixin.dart
index 0ef562c..1b8d651 100644
--- a/pkg/analyzer_plugin/lib/plugin/fix_mixin.dart
+++ b/pkg/analyzer_plugin/lib/plugin/fix_mixin.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/dart/analysis/results.dart';
 import 'package:analyzer/error/error.dart';
 import 'package:analyzer/src/dart/analysis/driver.dart';
diff --git a/pkg/analyzer_plugin/lib/plugin/folding_mixin.dart b/pkg/analyzer_plugin/lib/plugin/folding_mixin.dart
index 9a46c18..ecae950 100644
--- a/pkg/analyzer_plugin/lib/plugin/folding_mixin.dart
+++ b/pkg/analyzer_plugin/lib/plugin/folding_mixin.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/src/dart/analysis/driver.dart';
 import 'package:analyzer_plugin/plugin/plugin.dart';
 import 'package:analyzer_plugin/protocol/protocol.dart';
diff --git a/pkg/analyzer_plugin/lib/plugin/highlights_mixin.dart b/pkg/analyzer_plugin/lib/plugin/highlights_mixin.dart
index b7ace88..a74deba 100644
--- a/pkg/analyzer_plugin/lib/plugin/highlights_mixin.dart
+++ b/pkg/analyzer_plugin/lib/plugin/highlights_mixin.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/src/dart/analysis/driver.dart';
 import 'package:analyzer_plugin/plugin/plugin.dart';
 import 'package:analyzer_plugin/protocol/protocol.dart';
diff --git a/pkg/analyzer_plugin/lib/plugin/kythe_mixin.dart b/pkg/analyzer_plugin/lib/plugin/kythe_mixin.dart
index 9a4841a..353ec8d 100644
--- a/pkg/analyzer_plugin/lib/plugin/kythe_mixin.dart
+++ b/pkg/analyzer_plugin/lib/plugin/kythe_mixin.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/src/dart/analysis/driver.dart';
 import 'package:analyzer_plugin/plugin/plugin.dart';
 import 'package:analyzer_plugin/protocol/protocol.dart';
diff --git a/pkg/analyzer_plugin/lib/plugin/navigation_mixin.dart b/pkg/analyzer_plugin/lib/plugin/navigation_mixin.dart
index 0dfdfcc..fb215d7 100644
--- a/pkg/analyzer_plugin/lib/plugin/navigation_mixin.dart
+++ b/pkg/analyzer_plugin/lib/plugin/navigation_mixin.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/src/dart/analysis/driver.dart';
 import 'package:analyzer_plugin/plugin/plugin.dart';
 import 'package:analyzer_plugin/protocol/protocol.dart';
diff --git a/pkg/analyzer_plugin/lib/plugin/occurrences_mixin.dart b/pkg/analyzer_plugin/lib/plugin/occurrences_mixin.dart
index 3a087e3..7c2fd1e 100644
--- a/pkg/analyzer_plugin/lib/plugin/occurrences_mixin.dart
+++ b/pkg/analyzer_plugin/lib/plugin/occurrences_mixin.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/src/dart/analysis/driver.dart';
 import 'package:analyzer_plugin/plugin/plugin.dart';
 import 'package:analyzer_plugin/protocol/protocol.dart';
diff --git a/pkg/analyzer_plugin/lib/plugin/outline_mixin.dart b/pkg/analyzer_plugin/lib/plugin/outline_mixin.dart
index bab4dd3..b249718 100644
--- a/pkg/analyzer_plugin/lib/plugin/outline_mixin.dart
+++ b/pkg/analyzer_plugin/lib/plugin/outline_mixin.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/src/dart/analysis/driver.dart';
 import 'package:analyzer_plugin/plugin/plugin.dart';
 import 'package:analyzer_plugin/protocol/protocol.dart';
diff --git a/pkg/analyzer_plugin/lib/plugin/plugin.dart b/pkg/analyzer_plugin/lib/plugin/plugin.dart
index 4e8f153..970d5d9 100644
--- a/pkg/analyzer_plugin/lib/plugin/plugin.dart
+++ b/pkg/analyzer_plugin/lib/plugin/plugin.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/dart/analysis/results.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/file_system/physical_file_system.dart';
diff --git a/pkg/analyzer_plugin/lib/src/utilities/change_builder/change_builder_core.dart b/pkg/analyzer_plugin/lib/src/utilities/change_builder/change_builder_core.dart
index 38904ba..c16d12f 100644
--- a/pkg/analyzer_plugin/lib/src/utilities/change_builder/change_builder_core.dart
+++ b/pkg/analyzer_plugin/lib/src/utilities/change_builder/change_builder_core.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:collection';
 import 'dart:math' as math;
 
diff --git a/pkg/analyzer_plugin/lib/utilities/change_builder/change_builder_core.dart b/pkg/analyzer_plugin/lib/utilities/change_builder/change_builder_core.dart
index 7dd762e..0d0914f 100644
--- a/pkg/analyzer_plugin/lib/utilities/change_builder/change_builder_core.dart
+++ b/pkg/analyzer_plugin/lib/utilities/change_builder/change_builder_core.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/dart/analysis/session.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
diff --git a/pkg/analyzer_plugin/lib/utilities/change_builder/change_builder_dart.dart b/pkg/analyzer_plugin/lib/utilities/change_builder/change_builder_dart.dart
index 1b29916..fef21a1 100644
--- a/pkg/analyzer_plugin/lib/utilities/change_builder/change_builder_dart.dart
+++ b/pkg/analyzer_plugin/lib/utilities/change_builder/change_builder_dart.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/dart/analysis/session.dart';
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
diff --git a/pkg/analyzer_plugin/lib/utilities/completion/completion_core.dart b/pkg/analyzer_plugin/lib/utilities/completion/completion_core.dart
index 2defc81..0b192c3 100644
--- a/pkg/analyzer_plugin/lib/utilities/completion/completion_core.dart
+++ b/pkg/analyzer_plugin/lib/utilities/completion/completion_core.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/dart/analysis/results.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer_plugin/protocol/protocol.dart';
diff --git a/pkg/analyzer_plugin/lib/utilities/completion/inherited_reference_contributor.dart b/pkg/analyzer_plugin/lib/utilities/completion/inherited_reference_contributor.dart
index 3a76d3f..d18758d 100644
--- a/pkg/analyzer_plugin/lib/utilities/completion/inherited_reference_contributor.dart
+++ b/pkg/analyzer_plugin/lib/utilities/completion/inherited_reference_contributor.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
diff --git a/pkg/analyzer_plugin/lib/utilities/completion/type_member_contributor.dart b/pkg/analyzer_plugin/lib/utilities/completion/type_member_contributor.dart
index 2d8c195..f5630f1 100644
--- a/pkg/analyzer_plugin/lib/utilities/completion/type_member_contributor.dart
+++ b/pkg/analyzer_plugin/lib/utilities/completion/type_member_contributor.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
diff --git a/pkg/analyzer_plugin/test/plugin/assist_mixin_test.dart b/pkg/analyzer_plugin/test/plugin/assist_mixin_test.dart
index ea37ec5..67f2c28 100644
--- a/pkg/analyzer_plugin/test/plugin/assist_mixin_test.dart
+++ b/pkg/analyzer_plugin/test/plugin/assist_mixin_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/src/test_utilities/resource_provider_mixin.dart';
 import 'package:analyzer_plugin/plugin/assist_mixin.dart';
diff --git a/pkg/analyzer_plugin/test/plugin/completion_mixin_test.dart b/pkg/analyzer_plugin/test/plugin/completion_mixin_test.dart
index 13dcb82..36ce569 100644
--- a/pkg/analyzer_plugin/test/plugin/completion_mixin_test.dart
+++ b/pkg/analyzer_plugin/test/plugin/completion_mixin_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/src/test_utilities/resource_provider_mixin.dart';
 import 'package:analyzer_plugin/plugin/completion_mixin.dart';
diff --git a/pkg/analyzer_plugin/test/plugin/fix_mixin_test.dart b/pkg/analyzer_plugin/test/plugin/fix_mixin_test.dart
index 8e35430..578c0ae 100644
--- a/pkg/analyzer_plugin/test/plugin/fix_mixin_test.dart
+++ b/pkg/analyzer_plugin/test/plugin/fix_mixin_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/error/error.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/src/error/codes.dart';
diff --git a/pkg/analyzer_plugin/test/plugin/kythe_mixin_test.dart b/pkg/analyzer_plugin/test/plugin/kythe_mixin_test.dart
index f6b211f..45588b4 100644
--- a/pkg/analyzer_plugin/test/plugin/kythe_mixin_test.dart
+++ b/pkg/analyzer_plugin/test/plugin/kythe_mixin_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/src/test_utilities/resource_provider_mixin.dart';
 import 'package:analyzer_plugin/plugin/kythe_mixin.dart';
diff --git a/pkg/analyzer_plugin/test/plugin/plugin_test.dart b/pkg/analyzer_plugin/test/plugin/plugin_test.dart
index 0826036..92d227b 100644
--- a/pkg/analyzer_plugin/test/plugin/plugin_test.dart
+++ b/pkg/analyzer_plugin/test/plugin/plugin_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/src/dart/analysis/driver.dart';
 import 'package:analyzer/src/test_utilities/resource_provider_mixin.dart';
diff --git a/pkg/analyzer_plugin/test/src/channel/isolate_channel_test.dart b/pkg/analyzer_plugin/test/src/channel/isolate_channel_test.dart
index 5db397a..05b5876 100644
--- a/pkg/analyzer_plugin/test/src/channel/isolate_channel_test.dart
+++ b/pkg/analyzer_plugin/test/src/channel/isolate_channel_test.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:isolate';
 
 import 'package:analyzer_plugin/protocol/protocol.dart';
diff --git a/pkg/analyzer_plugin/test/src/utilities/change_builder/change_builder_dart_test.dart b/pkg/analyzer_plugin/test/src/utilities/change_builder/change_builder_dart_test.dart
index 2af81b8..764a691 100644
--- a/pkg/analyzer_plugin/test/src/utilities/change_builder/change_builder_dart_test.dart
+++ b/pkg/analyzer_plugin/test/src/utilities/change_builder/change_builder_dart_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/nullability_suffix.dart';
diff --git a/pkg/analyzer_plugin/test/src/utilities/change_builder/dart/import_library_element_test.dart b/pkg/analyzer_plugin/test/src/utilities/change_builder/dart/import_library_element_test.dart
index f108f1c..341d53a 100644
--- a/pkg/analyzer_plugin/test/src/utilities/change_builder/dart/import_library_element_test.dart
+++ b/pkg/analyzer_plugin/test/src/utilities/change_builder/dart/import_library_element_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
 import 'package:analyzer_plugin/utilities/change_builder/change_builder_core.dart';
 import 'package:test/test.dart';
diff --git a/pkg/analyzer_plugin/test/src/utilities/completion/completion_target_test.dart b/pkg/analyzer_plugin/test/src/utilities/completion/completion_target_test.dart
index dd47e63..8b94108 100644
--- a/pkg/analyzer_plugin/test/src/utilities/completion/completion_target_test.dart
+++ b/pkg/analyzer_plugin/test/src/utilities/completion/completion_target_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/src/generated/engine.dart' as analyzer;
diff --git a/pkg/analyzer_plugin/test/src/utilities/completion/optype_test.dart b/pkg/analyzer_plugin/test/src/utilities/completion/optype_test.dart
index f5970dd..7fc0527 100644
--- a/pkg/analyzer_plugin/test/src/utilities/completion/optype_test.dart
+++ b/pkg/analyzer_plugin/test/src/utilities/completion/optype_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
 import 'package:analyzer_plugin/src/utilities/completion/completion_target.dart';
 import 'package:analyzer_plugin/src/utilities/completion/optype.dart';
diff --git a/pkg/analyzer_plugin/test/support/abstract_context.dart b/pkg/analyzer_plugin/test/support/abstract_context.dart
index 373c7d0..4421f8c 100644
--- a/pkg/analyzer_plugin/test/support/abstract_context.dart
+++ b/pkg/analyzer_plugin/test/support/abstract_context.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/dart/analysis/session.dart';
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
diff --git a/pkg/analyzer_plugin/test/support/abstract_single_unit.dart b/pkg/analyzer_plugin/test/support/abstract_single_unit.dart
index 4e9efdb..94560b0 100644
--- a/pkg/analyzer_plugin/test/support/abstract_single_unit.dart
+++ b/pkg/analyzer_plugin/test/support/abstract_single_unit.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/error/error.dart';
diff --git a/pkg/analyzer_plugin/test/utilities/completion/type_member_contributor_test.dart b/pkg/analyzer_plugin/test/utilities/completion/type_member_contributor_test.dart
index de0ff2c..186ce86 100644
--- a/pkg/analyzer_plugin/test/utilities/completion/type_member_contributor_test.dart
+++ b/pkg/analyzer_plugin/test/utilities/completion/type_member_contributor_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
 import 'package:analyzer_plugin/utilities/completion/completion_core.dart';
 import 'package:analyzer_plugin/utilities/completion/relevance.dart';
diff --git a/pkg/dartdev/bin/dartdev.dart b/pkg/dartdev/bin/dartdev.dart
index 4e0f939..c2eee8a 100644
--- a/pkg/dartdev/bin/dartdev.dart
+++ b/pkg/dartdev/bin/dartdev.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:isolate';
 
 import 'package:dartdev/dartdev.dart';
diff --git a/pkg/dartfix/lib/listener/bad_message_listener.dart b/pkg/dartfix/lib/listener/bad_message_listener.dart
index b8fb5dc..03cb102 100644
--- a/pkg/dartfix/lib/listener/bad_message_listener.dart
+++ b/pkg/dartfix/lib/listener/bad_message_listener.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:analysis_server_client/listener/server_listener.dart';
 
 /// [BadMessageListener] throws an exception if the [Client] receives bad data.
diff --git a/pkg/dartfix/lib/src/driver.dart b/pkg/dartfix/lib/src/driver.dart
index 1bb0668..26f7ce93 100644
--- a/pkg/dartfix/lib/src/driver.dart
+++ b/pkg/dartfix/lib/src/driver.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:io' show File, Platform;
 
 import 'package:analysis_server_client/handler/connection_handler.dart';
diff --git a/pkg/nnbd_migration/lib/src/preview/dart_logo_page.dart b/pkg/nnbd_migration/lib/src/preview/dart_logo_page.dart
index 061ace1..009a671 100644
--- a/pkg/nnbd_migration/lib/src/preview/dart_logo_page.dart
+++ b/pkg/nnbd_migration/lib/src/preview/dart_logo_page.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:nnbd_migration/src/front_end/resources/resources.g.dart'
     as resources;
 import 'package:nnbd_migration/src/preview/preview_page.dart';
diff --git a/pkg/nnbd_migration/lib/src/preview/highlight_css_page.dart b/pkg/nnbd_migration/lib/src/preview/highlight_css_page.dart
index 7553358..5b13262 100644
--- a/pkg/nnbd_migration/lib/src/preview/highlight_css_page.dart
+++ b/pkg/nnbd_migration/lib/src/preview/highlight_css_page.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:nnbd_migration/src/front_end/resources/resources.g.dart'
     as resources;
 import 'package:nnbd_migration/src/preview/preview_page.dart';
diff --git a/pkg/nnbd_migration/lib/src/preview/highlight_js_page.dart b/pkg/nnbd_migration/lib/src/preview/highlight_js_page.dart
index 177266c..564c782 100644
--- a/pkg/nnbd_migration/lib/src/preview/highlight_js_page.dart
+++ b/pkg/nnbd_migration/lib/src/preview/highlight_js_page.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:nnbd_migration/src/front_end/resources/resources.g.dart'
     as resources;
 import 'package:nnbd_migration/src/preview/preview_page.dart';
diff --git a/pkg/nnbd_migration/lib/src/preview/http_preview_server.dart b/pkg/nnbd_migration/lib/src/preview/http_preview_server.dart
index 9c335ff..105b9f6 100644
--- a/pkg/nnbd_migration/lib/src/preview/http_preview_server.dart
+++ b/pkg/nnbd_migration/lib/src/preview/http_preview_server.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:io';
 
 import 'package:nnbd_migration/src/front_end/migration_state.dart';
diff --git a/pkg/nnbd_migration/lib/src/preview/material_icons_page.dart b/pkg/nnbd_migration/lib/src/preview/material_icons_page.dart
index 0364582..df3dc90 100644
--- a/pkg/nnbd_migration/lib/src/preview/material_icons_page.dart
+++ b/pkg/nnbd_migration/lib/src/preview/material_icons_page.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:nnbd_migration/src/front_end/resources/resources.g.dart'
     as resources;
 import 'package:nnbd_migration/src/preview/preview_page.dart';
diff --git a/pkg/nnbd_migration/lib/src/preview/pages.dart b/pkg/nnbd_migration/lib/src/preview/pages.dart
index 29defdb..5015846 100644
--- a/pkg/nnbd_migration/lib/src/preview/pages.dart
+++ b/pkg/nnbd_migration/lib/src/preview/pages.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
diff --git a/pkg/nnbd_migration/lib/src/preview/preview_page.dart b/pkg/nnbd_migration/lib/src/preview/preview_page.dart
index 23ca203..afc2aa1 100644
--- a/pkg/nnbd_migration/lib/src/preview/preview_page.dart
+++ b/pkg/nnbd_migration/lib/src/preview/preview_page.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:nnbd_migration/src/preview/pages.dart';
 import 'package:nnbd_migration/src/preview/preview_site.dart';
 
diff --git a/pkg/nnbd_migration/lib/src/preview/preview_site.dart b/pkg/nnbd_migration/lib/src/preview/preview_site.dart
index f77ee13..42b087e 100644
--- a/pkg/nnbd_migration/lib/src/preview/preview_site.dart
+++ b/pkg/nnbd_migration/lib/src/preview/preview_site.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 import 'dart:math';
diff --git a/pkg/nnbd_migration/lib/src/preview/roboto_mono_page.dart b/pkg/nnbd_migration/lib/src/preview/roboto_mono_page.dart
index 913ba72..dbcaeb0 100644
--- a/pkg/nnbd_migration/lib/src/preview/roboto_mono_page.dart
+++ b/pkg/nnbd_migration/lib/src/preview/roboto_mono_page.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:nnbd_migration/src/front_end/resources/resources.g.dart'
     as resources;
 import 'package:nnbd_migration/src/preview/preview_page.dart';
diff --git a/pkg/nnbd_migration/lib/src/preview/roboto_page.dart b/pkg/nnbd_migration/lib/src/preview/roboto_page.dart
index db4c92a..d7ea886 100644
--- a/pkg/nnbd_migration/lib/src/preview/roboto_page.dart
+++ b/pkg/nnbd_migration/lib/src/preview/roboto_page.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:nnbd_migration/src/front_end/resources/resources.g.dart'
     as resources;
 import 'package:nnbd_migration/src/preview/preview_page.dart';
diff --git a/pkg/nnbd_migration/lib/src/utilities/subprocess_launcher.dart b/pkg/nnbd_migration/lib/src/utilities/subprocess_launcher.dart
index 8147996..346b1e0 100644
--- a/pkg/nnbd_migration/lib/src/utilities/subprocess_launcher.dart
+++ b/pkg/nnbd_migration/lib/src/utilities/subprocess_launcher.dart
@@ -6,8 +6,6 @@
 // and extract into a separate package, generate testing and mirrors, and
 // reimport that into the SDK, before cut and paste gets out of hand.
 
-import 'dart:async';
-
 /// This is a modified version of dartdoc's
 /// SubprocessLauncher from test/src/utils.dart, for use with the
 /// nnbd_migration script.
diff --git a/pkg/vm_snapshot_analysis/CHANGELOG.md b/pkg/vm_snapshot_analysis/CHANGELOG.md
index 7506f91..135e095 100644
--- a/pkg/vm_snapshot_analysis/CHANGELOG.md
+++ b/pkg/vm_snapshot_analysis/CHANGELOG.md
@@ -5,6 +5,8 @@
 depth of outputted dependency trees configurable.
 - Rename `deps-collapse-depth` (formerly `-d`) flag for `summary` command to
 `deps-start-depth` (now `-s`).
+- Add `generateCallGraphWithDominators` method that generates a `CallGraph`
+object from precompiler trace.
 
 ## 0.5.4
 - Fix bug causing name clash for Type class.
diff --git a/pkg/vm_snapshot_analysis/lib/precompiler_trace.dart b/pkg/vm_snapshot_analysis/lib/precompiler_trace.dart
index 2cbcea2..2fec35e 100644
--- a/pkg/vm_snapshot_analysis/lib/precompiler_trace.dart
+++ b/pkg/vm_snapshot_analysis/lib/precompiler_trace.dart
@@ -105,21 +105,21 @@
 
   // Mapping from [ProgramInfoNode] to a corresponding [CallGraphNode] (if any)
   // via [ProgramInfoNode.id].
-  final List<CallGraphNode> _nodeByEntityId;
+  final List<CallGraphNode> _graphNodeByEntityId;
 
-  CallGraph._(this.program, this.nodes, this._nodeByEntityId);
+  CallGraph._(this.program, this.nodes, this._graphNodeByEntityId);
 
   CallGraphNode get root => nodes.first;
 
-  CallGraphNode lookup(ProgramInfoNode node) => _nodeByEntityId[node.id];
+  CallGraphNode lookup(ProgramInfoNode node) => _graphNodeByEntityId[node.id];
 
   Iterable<CallGraphNode> get dynamicCalls =>
       nodes.where((n) => n.isDynamicCallNode);
 
   /// Compute a collapsed version of the call-graph, where
   CallGraph collapse(NodeType type, {bool dropCallNodes = false}) {
-    final nodesByData = <Object, CallGraphNode>{};
-    final nodeByEntityId = <CallGraphNode>[];
+    final graphNodesByData = <Object, CallGraphNode>{};
+    final graphNodeByEntityId = <CallGraphNode>[];
 
     ProgramInfoNode collapsed(ProgramInfoNode nn) {
       // Root always collapses onto itself.
@@ -138,14 +138,14 @@
       return n;
     }
 
-    CallGraphNode nodeFor(Object data) {
-      return nodesByData.putIfAbsent(data, () {
-        final n = CallGraphNode(nodesByData.length, data: data);
+    CallGraphNode callGraphNodeFor(Object data) {
+      return graphNodesByData.putIfAbsent(data, () {
+        final n = CallGraphNode(graphNodesByData.length, data: data);
         if (data is ProgramInfoNode) {
-          if (nodeByEntityId.length <= data.id) {
-            nodeByEntityId.length = data.id * 2 + 1;
+          if (graphNodeByEntityId.length <= data.id) {
+            graphNodeByEntityId.length = data.id * 2 + 1;
           }
-          nodeByEntityId[data.id] = n;
+          graphNodeByEntityId[data.id] = n;
         }
         return n;
       });
@@ -153,9 +153,9 @@
 
     final newNodes = nodes.map((n) {
       if (n.data is ProgramInfoNode) {
-        return nodeFor(collapsed(n.data));
+        return callGraphNodeFor(collapsed(n.data));
       } else if (!dropCallNodes) {
-        return nodeFor(n.data);
+        return callGraphNodeFor(n.data);
       }
     }).toList(growable: false);
 
@@ -170,8 +170,8 @@
       }
     }
 
-    return CallGraph._(
-        program, nodesByData.values.toList(growable: false), nodeByEntityId);
+    return CallGraph._(program, graphNodesByData.values.toList(growable: false),
+        graphNodeByEntityId);
   }
 
   /// Compute dominator tree of the call-graph.
@@ -529,3 +529,21 @@
         name: libraryUri, parent: node, type: NodeType.libraryNode);
   }
 }
+
+/// Generates a [CallGraph] from the given [precompilerTrace], which is produced
+/// by `--trace-precompiler-to`, then collapses it down to the granularity
+/// specified by [nodeType], and computes dominators of the resulting graph.
+CallGraph generateCallGraphWithDominators(
+  Object precompilerTrace,
+  NodeType nodeType,
+) {
+  var callGraph = loadTrace(precompilerTrace);
+
+  // Convert call graph into the approximate dependency graph, dropping any
+  // dynamic and dispatch table based dependencies from the graph and only
+  // following the static call, field access and allocation edges.
+  callGraph = callGraph.collapse(nodeType, dropCallNodes: true)
+    ..computeDominators();
+
+  return callGraph;
+}
diff --git a/pkg/vm_snapshot_analysis/lib/src/commands/summary.dart b/pkg/vm_snapshot_analysis/lib/src/commands/summary.dart
index 7809aa4..13854d2 100644
--- a/pkg/vm_snapshot_analysis/lib/src/commands/summary.dart
+++ b/pkg/vm_snapshot_analysis/lib/src/commands/summary.dart
@@ -187,17 +187,13 @@
       (granularity == HistogramType.byLibrary ||
           granularity == HistogramType.byPackage)) {
     final traceJsonRaw = await loadJsonFromFile(traceJson);
-    var callGraph = loadTrace(traceJsonRaw);
 
-    // Convert call graph into the approximate dependency graph, dropping any
-    // dynamic and dispatch table based dependencies from the graph and only
-    // following the static call, field access and allocation edges.
-    callGraph = callGraph.collapse(
-        granularity == HistogramType.byLibrary
-            ? NodeType.libraryNode
-            : NodeType.packageNode,
-        dropCallNodes: true);
-    callGraph.computeDominators();
+    final callGraph = generateCallGraphWithDominators(
+      traceJsonRaw,
+      granularity == HistogramType.byLibrary
+          ? NodeType.libraryNode
+          : NodeType.packageNode,
+    );
 
     // Compute name mapping from histogram buckets to new coarser buckets, by
     // collapsing dependency tree at [depsStartDepth] level: node 'Foo' with
diff --git a/pkg/vm_snapshot_analysis/pubspec.yaml b/pkg/vm_snapshot_analysis/pubspec.yaml
index dd0da7e..eb64977 100644
--- a/pkg/vm_snapshot_analysis/pubspec.yaml
+++ b/pkg/vm_snapshot_analysis/pubspec.yaml
@@ -1,6 +1,6 @@
 name: vm_snapshot_analysis
 description: Utilities for analysing AOT snapshot size.
-version: 0.5.5-dev.1
+version: 0.5.5
 
 homepage: https://github.com/dart-lang/sdk/tree/master/pkg/vm_snapshot_analysis
 
diff --git a/runtime/vm/os_fuchsia.cc b/runtime/vm/os_fuchsia.cc
index 6ad304e..0a9ffa1 100644
--- a/runtime/vm/os_fuchsia.cc
+++ b/runtime/vm/os_fuchsia.cc
@@ -353,7 +353,7 @@
 }
 
 void OS::Init() {
-  if (async_get_default_dispatcher() == NULL) {
+  if (async_get_default_dispatcher() == nullptr) {
     async_loop_create(&kAsyncLoopConfigAttachToCurrentThread, &message_loop);
     async_set_default_dispatcher(async_loop_get_dispatcher(message_loop));
     async_loop_start_thread(message_loop, "Fuchsia async loop", nullptr);
@@ -368,9 +368,19 @@
 }
 
 void OS::Cleanup() {
+  if (message_loop != nullptr) {
+    async_loop_shutdown(message_loop);
+  }
+
   metrics = nullptr;
   component_inspector = nullptr;
+
   if (message_loop != nullptr) {
+    // Check message_loop is still the default dispatcher before clearing it.
+    if (async_get_default_dispatcher() ==
+        async_loop_get_dispatcher(message_loop)) {
+      async_set_default_dispatcher(nullptr);
+    }
     async_loop_destroy(message_loop);
     message_loop = nullptr;
   }
diff --git a/tests/language/extension_methods/static_extension_getter_setter_conflicts_test.dart b/tests/language/extension_methods/static_extension_getter_setter_conflicts_test.dart
index 42c9c65..abb4bb3 100644
--- a/tests/language/extension_methods/static_extension_getter_setter_conflicts_test.dart
+++ b/tests/language/extension_methods/static_extension_getter_setter_conflicts_test.dart
@@ -109,7 +109,7 @@
 
   c1a.m1 = 0;
   //  ^^
-  // [analyzer] COMPILE_TIME_ERROR.ASSIGNMENT_TO_FINAL_LOCAL
+  // [analyzer] COMPILE_TIME_ERROR.ASSIGNMENT_TO_FINAL_NO_SETTER
   // [cfe] The setter 'm1' isn't defined for the class 'C1<int>'.
 
   c1a.m2;
@@ -195,7 +195,7 @@
 
   c1c.m1 = 0;
   //  ^^
-  // [analyzer] COMPILE_TIME_ERROR.ASSIGNMENT_TO_FINAL_LOCAL
+  // [analyzer] COMPILE_TIME_ERROR.ASSIGNMENT_TO_FINAL_NO_SETTER
   // [cfe] The setter 'm1' isn't defined for the class 'C1<Object>'.
 
   c1c.m2;
diff --git a/tests/language_2/extension_methods/static_extension_getter_setter_conflicts_test.dart b/tests/language_2/extension_methods/static_extension_getter_setter_conflicts_test.dart
index 4986f45..7009a05 100644
--- a/tests/language_2/extension_methods/static_extension_getter_setter_conflicts_test.dart
+++ b/tests/language_2/extension_methods/static_extension_getter_setter_conflicts_test.dart
@@ -109,7 +109,7 @@
 
   c1a.m1 = 0;
   //  ^^
-  // [analyzer] COMPILE_TIME_ERROR.ASSIGNMENT_TO_FINAL_LOCAL
+  // [analyzer] COMPILE_TIME_ERROR.ASSIGNMENT_TO_FINAL_NO_SETTER
   // [cfe] The setter 'm1' isn't defined for the class 'C1<int>'.
 
   c1a.m2;
diff --git a/tools/VERSION b/tools/VERSION
index 193d231..69a8be3 100644
--- a/tools/VERSION
+++ b/tools/VERSION
@@ -27,5 +27,5 @@
 MAJOR 2
 MINOR 10
 PATCH 0
-PRERELEASE 89
+PRERELEASE 90
 PRERELEASE_PATCH 0
\ No newline at end of file