Remove unused imports (#657)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index d13790d..3a15d73 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 0.12.23+1
+
+* Remove unused imports. 
+
 ## 0.12.23
 
 * Add a `fold_stack_frames` field for `dart_test.yaml`. This will
diff --git a/analysis_options.yaml b/analysis_options.yaml
index 542aff2..ea7fd22 100644
--- a/analysis_options.yaml
+++ b/analysis_options.yaml
@@ -1,5 +1,14 @@
 analyzer:
   strong-mode: true
+# Upgrade lints to errors that will break Google3
+errors:
+  unused_element: error
+  unused_import: error
+  unused_local_variable: error
+  dead_code: error
+  ### Useful to uncomment during development to remove the noise of the many
+  ### deprecated APIs.
+  # deprecated_member_use: ignore
 linter:
   rules:
     - await_only_futures
diff --git a/lib/src/frontend/stream_matcher.dart b/lib/src/frontend/stream_matcher.dart
index 9e166ca..8392d96 100644
--- a/lib/src/frontend/stream_matcher.dart
+++ b/lib/src/frontend/stream_matcher.dart
@@ -8,7 +8,6 @@
 import 'package:matcher/matcher.dart';
 
 import '../utils.dart';
-import '../backend/invoker.dart';
 import 'test_chain.dart';
 import 'async_matcher.dart';
 
diff --git a/lib/src/frontend/throws_matcher.dart b/lib/src/frontend/throws_matcher.dart
index 75c5d23..c0164ae 100644
--- a/lib/src/frontend/throws_matcher.dart
+++ b/lib/src/frontend/throws_matcher.dart
@@ -9,7 +9,6 @@
 import '../utils.dart';
 import 'async_matcher.dart';
 import '../frontend/test_chain.dart';
-import '../backend/invoker.dart';
 
 /// This function is deprecated.
 ///
diff --git a/lib/src/runner/reporter/json.dart b/lib/src/runner/reporter/json.dart
index fba28a6..d8c2335 100644
--- a/lib/src/runner/reporter/json.dart
+++ b/lib/src/runner/reporter/json.dart
@@ -13,7 +13,6 @@
 import '../../backend/suite.dart';
 import '../../backend/test_platform.dart';
 import '../../frontend/expect.dart';
-import '../../utils.dart';
 import '../configuration.dart';
 import '../configuration/suite.dart';
 import '../engine.dart';
diff --git a/pubspec.yaml b/pubspec.yaml
index c91bf4c..ffdacea 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: test
-version: 0.12.23
+version: 0.12.23+1
 author: Dart Team <misc@dartlang.org>
 description: A library for writing dart unit tests.
 homepage: https://github.com/dart-lang/test