diff --git a/pkg/front_end/lib/src/api_prototype/incremental_kernel_generator.dart b/pkg/front_end/lib/src/api_prototype/incremental_kernel_generator.dart
index 12614bb..a6d071f 100644
--- a/pkg/front_end/lib/src/api_prototype/incremental_kernel_generator.dart
+++ b/pkg/front_end/lib/src/api_prototype/incremental_kernel_generator.dart
@@ -42,7 +42,7 @@
   /// Notice that the component has to include the platform, and that no other
   /// platform will be loaded.
   factory IncrementalKernelGenerator.fromComponent(
-      CompilerOptions options, Uri entryPoint, Component component,
+      CompilerOptions options, Uri entryPoint, Component? component,
       [bool? outlineOnly, IncrementalSerializer? incrementalSerializer]) {
     return new IncrementalCompiler.fromComponent(
         new CompilerContext(
@@ -72,7 +72,7 @@
 
   /// Returns a component whose libraries are the recompiled libraries,
   /// or - in the case of [fullComponent] - a full Component.
-  Future<Component> computeDelta({List<Uri> entryPoints, bool fullComponent});
+  Future<Component> computeDelta({List<Uri>? entryPoints, bool fullComponent});
 
   /// Returns [CoreTypes] used during compilation.
   /// Valid after [computeDelta] is called.
@@ -136,7 +136,7 @@
       List<TypeParameter> typeDefinitions,
       String syntheticProcedureName,
       Uri libraryUri,
-      [String className,
+      [String? className,
       bool isStatic = false]);
 
   /// Sets experimental features.
diff --git a/pkg/front_end/lib/src/api_unstable/bazel_worker.dart b/pkg/front_end/lib/src/api_unstable/bazel_worker.dart
index 46566f1..8cf810b 100644
--- a/pkg/front_end/lib/src/api_unstable/bazel_worker.dart
+++ b/pkg/front_end/lib/src/api_unstable/bazel_worker.dart
@@ -58,7 +58,7 @@
 /// Re-uses cached components from [oldState.workerInputCache], and reloads them
 /// as necessary based on [workerInputDigests].
 Future<InitializedCompilerState> initializeIncrementalCompiler(
-    InitializedCompilerState oldState,
+    InitializedCompilerState? oldState,
     Set<String> tags,
     Uri sdkSummary,
     Uri packagesFile,
@@ -99,7 +99,7 @@
 }
 
 Future<InitializedCompilerState> initializeCompiler(
-  InitializedCompilerState oldState,
+  InitializedCompilerState? oldState,
   Uri sdkSummary,
   Uri librariesSpecificationUri,
   Uri packagesFile,
diff --git a/pkg/vm/lib/incremental_compiler.dart b/pkg/vm/lib/incremental_compiler.dart
index 5179a44..a8d3271 100644
--- a/pkg/vm/lib/incremental_compiler.dart
+++ b/pkg/vm/lib/incremental_compiler.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.
 
-// @dart=2.9
-
 /// Defines wrapper class around incremental compiler to support
 /// the flow, where incremental deltas can be rejected by VM.
 import 'dart:async';
@@ -20,23 +18,23 @@
 /// deltas and combines them together into resultant program until it is
 /// accepted.
 class IncrementalCompiler {
-  IncrementalKernelGenerator _generator;
-  IncrementalSerializer incrementalSerializer;
+  late IncrementalKernelGenerator _generator;
+  IncrementalSerializer? incrementalSerializer;
 
   // Component that reflect the state that was most recently accepted by the
   // client. Is [null], if no compilation results were accepted by the client.
-  Component _lastKnownGood;
-  List<Component> _pendingDeltas;
+  Component? _lastKnownGood;
+  late List<Component> _pendingDeltas;
   CompilerOptions _compilerOptions;
   bool initialized = false;
   bool fullComponent = false;
-  Uri initializeFromDillUri;
+  Uri? initializeFromDillUri;
   Uri _entryPoint;
   final bool forExpressionCompilationOnly;
 
   Uri get entryPoint => _entryPoint;
   IncrementalKernelGenerator get generator => _generator;
-  Component get lastKnownGoodComponent => _lastKnownGood;
+  Component? get lastKnownGoodComponent => _lastKnownGood;
 
   IncrementalCompiler(this._compilerOptions, this._entryPoint,
       {this.initializeFromDillUri, bool incrementalSerialization: true})
@@ -61,12 +59,12 @@
   ///
   /// If [entryPoint] is specified, that points to new entry point for the
   /// compilation. Otherwise, previously set entryPoint is used.
-  Future<Component> compile({Uri entryPoint}) async {
+  Future<Component> compile({Uri? entryPoint}) async {
     final task = new TimelineTask();
     try {
       task.start("IncrementalCompiler.compile");
       _entryPoint = entryPoint ?? _entryPoint;
-      List<Uri> entryPoints;
+      List<Uri>? entryPoints;
       if (entryPoint != null) entryPoints = [entryPoint];
       Component component = await _generator.computeDelta(
           entryPoints: entryPoints, fullComponent: fullComponent);
@@ -80,8 +78,9 @@
   }
 
   _combinePendingDeltas(bool includePlatform) {
-    Procedure mainMethod;
-    NonNullableByDefaultCompiledMode compilationMode;
+    Procedure? mainMethod;
+    NonNullableByDefaultCompiledMode compilationMode =
+        NonNullableByDefaultCompiledMode.Invalid;
     Map<Uri, Library> combined = <Uri, Library>{};
     Map<Uri, Source> uriToSource = new Map<Uri, Source>();
     for (Component delta in _pendingDeltas) {
@@ -104,8 +103,8 @@
       ..setMainMethodAndMode(mainMethod?.reference, true, compilationMode);
   }
 
-  CoreTypes getCoreTypes() => _generator.getCoreTypes();
-  ClassHierarchy getClassHierarchy() => _generator.getClassHierarchy();
+  CoreTypes? getCoreTypes() => _generator.getCoreTypes();
+  ClassHierarchy? getClassHierarchy() => _generator.getClassHierarchy();
 
   /// This lets incremental compiler know that results of last [compile] call
   /// were accepted, don't need to be included into subsequent [compile] calls
@@ -118,13 +117,14 @@
     Map<Uri, Library> combined = <Uri, Library>{};
     Map<Uri, Source> uriToSource = <Uri, Source>{};
 
-    if (_lastKnownGood != null) {
+    Component? lastKnownGood = _lastKnownGood;
+    if (lastKnownGood != null) {
       // TODO(aam): Figure out how to skip no-longer-used libraries from
       // [_lastKnownGood] libraries.
-      for (Library library in _lastKnownGood.libraries) {
+      for (Library library in lastKnownGood.libraries) {
         combined[library.importUri] = library;
       }
-      uriToSource.addAll(_lastKnownGood.uriToSource);
+      uriToSource.addAll(lastKnownGood.uriToSource);
     }
 
     Component candidate = _combinePendingDeltas(true);
@@ -133,13 +133,13 @@
     }
     uriToSource.addAll(candidate.uriToSource);
 
-    _lastKnownGood = new Component(
+    _lastKnownGood = lastKnownGood = new Component(
       libraries: combined.values.toList(),
       uriToSource: uriToSource,
     )..setMainMethodAndMode(
         candidate.mainMethod?.reference, true, candidate.mode);
     for (final repo in candidate.metadata.values) {
-      _lastKnownGood.addMetadataRepository(repo);
+      lastKnownGood.addMetadataRepository(repo);
     }
     _pendingDeltas.clear();
   }
@@ -182,12 +182,12 @@
     fullComponent = true;
   }
 
-  Future<Procedure> compileExpression(
+  Future<Procedure?> compileExpression(
       String expression,
       List<String> definitions,
       List<String> typeDefinitions,
       String libraryUri,
-      String klass,
+      String? klass,
       bool isStatic) {
     Map<String, DartType> completeDefinitions = {};
     for (String name in definitions) {
@@ -202,7 +202,6 @@
     }
 
     Uri library = Uri.parse(libraryUri);
-    if (library == null) return null;
 
     return _generator.compileExpression(expression, completeDefinitions,
         typeParameters, kDebugProcedureName, library, klass, isStatic);
diff --git a/pkg/vm/lib/kernel_front_end.dart b/pkg/vm/lib/kernel_front_end.dart
index 43d5a59..51ed004 100644
--- a/pkg/vm/lib/kernel_front_end.dart
+++ b/pkg/vm/lib/kernel_front_end.dart
@@ -2,10 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart=2.9
-
 /// Defines the VM-specific translation of Dart source code to kernel binaries.
-library vm.kernel_front_end;
 
 import 'dart:async';
 import 'dart:io' show File, IOSink;
@@ -162,7 +159,7 @@
 /// Run kernel compiler tool with given [options] and [usage]
 /// and return exit code.
 Future<int> runCompiler(ArgResults options, String usage) async {
-  final String platformKernel = options['platform'];
+  final String? platformKernel = options['platform'];
 
   if (options['help']) {
     print(usage);
@@ -176,26 +173,26 @@
 
   final String input = options.rest.single;
   final String outputFileName = options['output'] ?? "$input.dill";
-  final String packages = options['packages'];
+  final String? packages = options['packages'];
   final String targetName = options['target'];
-  final String fileSystemScheme = options['filesystem-scheme'];
-  final String depfile = options['depfile'];
-  final String fromDillFile = options['from-dill'];
-  final List<String> fileSystemRoots = options['filesystem-root'];
+  final String? fileSystemScheme = options['filesystem-scheme'];
+  final String? depfile = options['depfile'];
+  final String? fromDillFile = options['from-dill'];
+  final List<String>? fileSystemRoots = options['filesystem-root'];
   final bool aot = options['aot'];
   final bool tfa = options['tfa'];
   final bool linkPlatform = options['link-platform'];
   final bool embedSources = options['embed-sources'];
   final bool enableAsserts = options['enable-asserts'];
-  final bool nullSafety = options['sound-null-safety'];
+  final bool? nullSafety = options['sound-null-safety'];
   final bool useProtobufTreeShakerV2 = options['protobuf-tree-shaker-v2'];
   final bool splitOutputByPackages = options['split-output-by-packages'];
-  final String manifestFilename = options['manifest'];
-  final String dataDir = options['component-name'] ?? options['data-dir'];
+  final String? manifestFilename = options['manifest'];
+  final String? dataDir = options['component-name'] ?? options['data-dir'];
 
   final bool minimalKernel = options['minimal-kernel'];
   final bool treeShakeWriteOnlyFields = options['tree-shake-write-only-fields'];
-  final List<String> experimentalFlags = options['enable-experiment'];
+  final List<String>? experimentalFlags = options['enable-experiment'];
   final Map<String, String> environmentDefines = {};
 
   if (!parseCommandLineDefines(options['define'], environmentDefines, usage)) {
@@ -217,7 +214,7 @@
   final fileSystem =
       createFrontEndFileSystem(fileSystemScheme, fileSystemRoots);
 
-  final Uri packagesUri = packages != null ? resolveInputUri(packages) : null;
+  final Uri? packagesUri = packages != null ? resolveInputUri(packages) : null;
 
   final platformKernelUri = Uri.base.resolveUri(new Uri.file(platformKernel));
   final List<Uri> additionalDills = <Uri>[];
@@ -232,7 +229,8 @@
 
   final verbosity = Verbosity.parseArgument(options['verbosity']);
   final errorPrinter = new ErrorPrinter(verbosity);
-  final errorDetector = new ErrorDetector(previousErrorHandler: errorPrinter);
+  final errorDetector =
+      new ErrorDetector(previousErrorHandler: errorPrinter.call);
 
   final CompilerOptions compilerOptions = new CompilerOptions()
     ..sdkSummary = platformKernelUri
@@ -280,19 +278,20 @@
 
   errorPrinter.printCompilationMessages();
 
-  if (errorDetector.hasCompilationErrors || (results.component == null)) {
+  final Component? component = results.component;
+  if (errorDetector.hasCompilationErrors || (component == null)) {
     return compileTimeErrorExitCode;
   }
 
   final IOSink sink = new File(outputFileName).openWrite();
   final BinaryPrinter printer = new BinaryPrinter(sink,
       libraryFilter: (lib) => !results.loadedLibraries.contains(lib));
-  printer.writeComponentFile(results.component);
+  printer.writeComponentFile(component);
   await sink.close();
 
   if (depfile != null) {
     await writeDepfile(
-        fileSystem, results.compiledSources, outputFileName, depfile);
+        fileSystem, results.compiledSources!, outputFileName, depfile);
   }
 
   if (splitOutputByPackages) {
@@ -314,14 +313,14 @@
 /// Results of [compileToKernel]: generated kernel [Component] and
 /// collection of compiled sources.
 class KernelCompilationResults {
-  final Component component;
+  final Component? component;
 
   /// Set of libraries loaded from .dill, with or without the SDK depending on
   /// the compilation settings.
   final Set<Library> loadedLibraries;
-  final ClassHierarchy classHierarchy;
-  final CoreTypes coreTypes;
-  final Iterable<Uri> compiledSources;
+  final ClassHierarchy? classHierarchy;
+  final CoreTypes? coreTypes;
+  final Iterable<Uri>? compiledSources;
 
   KernelCompilationResults(this.component, this.loadedLibraries,
       this.classHierarchy, this.coreTypes, this.compiledSources);
@@ -338,29 +337,30 @@
     List<String> deleteToStringPackageUris: const <String>[],
     bool aot: false,
     bool useGlobalTypeFlowAnalysis: false,
-    Map<String, String> environmentDefines,
+    required Map<String, String> environmentDefines,
     bool enableAsserts: true,
     bool useProtobufTreeShakerV2: false,
     bool minimalKernel: false,
     bool treeShakeWriteOnlyFields: false,
-    String fromDillFile: null}) async {
+    String? fromDillFile: null}) async {
   // Replace error handler to detect if there are compilation errors.
   final errorDetector =
       new ErrorDetector(previousErrorHandler: options.onDiagnostic);
-  options.onDiagnostic = errorDetector;
+  options.onDiagnostic = errorDetector.call;
 
+  final target = options.target!;
   options.environmentDefines =
-      options.target.updateEnvironmentDefines(environmentDefines);
+      target.updateEnvironmentDefines(environmentDefines);
 
-  CompilerResult compilerResult;
+  CompilerResult? compilerResult;
   if (fromDillFile != null) {
     compilerResult =
         await loadKernel(options.fileSystem, resolveInputUri(fromDillFile));
   } else {
     compilerResult = await kernelForProgram(source, options);
   }
-  Component component = compilerResult?.component;
-  Iterable<Uri> compiledSources = component?.uriToSource?.keys;
+  final Component? component = compilerResult?.component;
+  Iterable<Uri>? compiledSources = component?.uriToSource.keys;
 
   Set<Library> loadedLibraries = createLoadedLibrariesSet(
       compilerResult?.loadedComponents, compilerResult?.sdkComponent,
@@ -373,13 +373,8 @@
 
   // Run global transformations only if component is correct.
   if ((aot || minimalKernel) && component != null) {
-    await runGlobalTransformations(
-        options.target,
-        component,
-        useGlobalTypeFlowAnalysis,
-        enableAsserts,
-        useProtobufTreeShakerV2,
-        errorDetector,
+    await runGlobalTransformations(target, component, useGlobalTypeFlowAnalysis,
+        enableAsserts, useProtobufTreeShakerV2, errorDetector,
         minimalKernel: minimalKernel,
         treeShakeWriteOnlyFields: treeShakeWriteOnlyFields);
 
@@ -387,7 +382,7 @@
       // compiledSources is component.uriToSource.keys.
       // Make a copy of compiledSources to detach it from
       // component.uriToSource which is cleared below.
-      compiledSources = compiledSources.toList();
+      compiledSources = compiledSources!.toList();
 
       component.metadata.clear();
       component.uriToSource.clear();
@@ -406,7 +401,7 @@
 }
 
 Set<Library> createLoadedLibrariesSet(
-    List<Component> loadedComponents, Component sdkComponent,
+    List<Component>? loadedComponents, Component? sdkComponent,
     {bool includePlatform: false}) {
   final Set<Library> loadedLibraries = {};
   if (loadedComponents != null) {
@@ -481,8 +476,11 @@
 
 /// Runs given [action] with [CompilerContext]. This is needed to
 /// be able to report compile-time errors.
-Future<T> runWithFrontEndCompilerContext<T>(Uri source,
-    CompilerOptions compilerOptions, Component component, T action()) async {
+Future<T> runWithFrontEndCompilerContext<T>(
+    Uri source,
+    CompilerOptions compilerOptions,
+    Component component,
+    Future<T> action()) async {
   final processedOptions =
       new ProcessedOptions(options: compilerOptions, inputs: [source]);
 
@@ -498,7 +496,7 @@
 }
 
 class ErrorDetector {
-  final DiagnosticMessageHandler previousErrorHandler;
+  final DiagnosticMessageHandler? previousErrorHandler;
   bool hasCompilationErrors = false;
 
   ErrorDetector({this.previousErrorHandler});
@@ -514,8 +512,9 @@
 
 class ErrorPrinter {
   final Verbosity verbosity;
-  final DiagnosticMessageHandler previousErrorHandler;
-  final compilationMessages = <Uri, List<DiagnosticMessage>>{};
+  final DiagnosticMessageHandler? previousErrorHandler;
+  final Map<Uri?, List<DiagnosticMessage>> compilationMessages =
+      <Uri?, List<DiagnosticMessage>>{};
 
   ErrorPrinter(this.verbosity, {this.previousErrorHandler});
 
@@ -539,8 +538,8 @@
         }
         return 0;
       });
-    for (final Uri sourceUri in sortedUris) {
-      for (final DiagnosticMessage message in compilationMessages[sourceUri]) {
+    for (final Uri? sourceUri in sortedUris) {
+      for (final DiagnosticMessage message in compilationMessages[sourceUri]!) {
         if (Verbosity.shouldPrint(verbosity, message)) {
           printDiagnosticMessage(message, print);
         }
@@ -576,7 +575,7 @@
 }
 
 /// Create front-end target with given name.
-Target createFrontEndTarget(String targetName,
+Target? createFrontEndTarget(String targetName,
     {bool trackWidgetCreation = false, bool nullSafety = false}) {
   // Make sure VM-specific targets are available.
   installAdditionalTargets();
@@ -591,9 +590,8 @@
 /// If requested, create a virtual mutli-root file system and/or an http aware
 /// file system.
 FileSystem createFrontEndFileSystem(
-    String multiRootFileSystemScheme, List<String> multiRootFileSystemRoots,
-    {bool allowHttp}) {
-  allowHttp ??= false;
+    String? multiRootFileSystemScheme, List<String>? multiRootFileSystemRoots,
+    {bool allowHttp = false}) {
   FileSystem fileSystem = StandardFileSystem.instance;
   if (allowHttp) {
     fileSystem = HttpAwareFileSystem(fileSystem);
@@ -615,7 +613,7 @@
 Future<Uri> asFileUri(FileSystem fileSystem, Uri uri) async {
   FileSystemEntity fse = fileSystem.entityForUri(uri);
   if (fse is MultiRootFileSystemEntity) {
-    fse = await (fse as MultiRootFileSystemEntity).delegate;
+    fse = await fse.delegate;
   }
   return fse.uri;
 }
@@ -645,8 +643,9 @@
 Future writeOutputSplitByPackages(Uri source, CompilerOptions compilerOptions,
     KernelCompilationResults compilationResults, String outputFileName) async {
   final packages = <String>[];
-  await runWithFrontEndCompilerContext(
-      source, compilerOptions, compilationResults.component, () async {
+  final Component component = compilationResults.component!;
+  await runWithFrontEndCompilerContext(source, compilerOptions, component,
+      () async {
     // When loading a kernel file list, flutter_runner and dart_runner expect
     // 'main' to be last.
     await forEachPackage(compilationResults,
@@ -655,12 +654,10 @@
       final String filename = '$outputFileName-$package.dilp';
       final IOSink sink = new File(filename).openWrite();
 
-      Component partComponent = compilationResults.component;
-
       final BinaryPrinter printer = new BinaryPrinter(sink,
           libraryFilter: (lib) =>
               packageFor(lib, compilationResults.loadedLibraries) == package);
-      printer.writeComponentFile(partComponent);
+      printer.writeComponentFile(component);
 
       await sink.close();
     }, mainFirst: false);
@@ -673,7 +670,7 @@
   await packagesList.close();
 }
 
-String packageFor(Library lib, Set<Library> loadedLibraries) {
+String? packageFor(Library lib, Set<Library> loadedLibraries) {
   // Core libraries are not written into any package kernel binaries.
   if (loadedLibraries.contains(lib)) return null;
 
@@ -701,23 +698,25 @@
   }
 }
 
-Future<Null> forEachPackage<T>(KernelCompilationResults results,
-    T action(String package, List<Library> libraries),
-    {bool mainFirst}) async {
-  final Component component = results.component;
+Future<void> forEachPackage(KernelCompilationResults results,
+    Future<void> action(String package, List<Library> libraries),
+    {required bool mainFirst}) async {
+  final Component component = results.component!;
   final Set<Library> loadedLibraries = results.loadedLibraries;
   sortComponent(component);
 
-  final packages = new Map<String, List<Library>>();
+  final Map<String, List<Library>> packages = <String, List<Library>>{};
   packages['main'] = <Library>[]; // Always create 'main'.
   for (Library lib in component.libraries) {
-    packages
-        .putIfAbsent(packageFor(lib, loadedLibraries), () => <Library>[])
-        .add(lib);
+    final String? package = packageFor(lib, loadedLibraries);
+    // Ignore external libraries.
+    if (package == null) {
+      continue;
+    }
+    packages.putIfAbsent(package, () => <Library>[]).add(lib);
   }
-  packages.remove(null); // Ignore external libraries.
 
-  final mainLibraries = packages.remove('main');
+  final mainLibraries = packages.remove('main')!;
   if (mainFirst) {
     await action('main', mainLibraries);
   }
@@ -728,7 +727,7 @@
   component.setMainMethodAndMode(null, true, compilationMode);
   component.problemsAsJson = null;
   for (String package in packages.keys) {
-    await action(package, packages[package]);
+    await action(package, packages[package]!);
   }
   component.setMainMethodAndMode(mainMethod?.reference, true, compilationMode);
   component.problemsAsJson = problemsAsJson;
@@ -750,8 +749,8 @@
   file.write(_escapePath(output));
   file.write(':');
   for (Uri dep in compiledSources) {
-    // Skip empty or corelib dependencies.
-    if (dep == null || dep.scheme == 'org-dartlang-sdk') continue;
+    // Skip corelib dependencies.
+    if (dep.scheme == 'org-dartlang-sdk') continue;
     Uri uri = await asFileUri(fileSystem, dep);
     file.write(' ');
     file.write(_escapePath(uri.toFilePath()));
@@ -761,7 +760,7 @@
 }
 
 Future<void> createFarManifest(
-    String output, String dataDir, String packageManifestFilename) async {
+    String output, String? dataDir, String packageManifestFilename) async {
   List<String> packages = await File('$output-packages').readAsLines();
 
   // Make sure the 'main' package is the last (convention with package loader).
@@ -791,7 +790,7 @@
     'typed_data',
     'vector_math'
   ]) {
-    Digest digest;
+    Digest? digest;
     if (packages.contains(package)) {
       final filenameInBuild = '$output-$package.dilp';
       final bytes = await File(filenameInBuild).readAsBytes();
@@ -813,11 +812,20 @@
 
   CompilerResultLoadedFromKernel(this.component);
 
-  List<int> get summary => null;
+  @override
+  List<int>? get summary => null;
+
+  @override
   List<Component> get loadedComponents => const <Component>[];
+
+  @override
   List<Uri> get deps => const <Uri>[];
-  CoreTypes get coreTypes => null;
-  ClassHierarchy get classHierarchy => null;
+
+  @override
+  CoreTypes? get coreTypes => null;
+
+  @override
+  ClassHierarchy? get classHierarchy => null;
 }
 
 Future<CompilerResult> loadKernel(
diff --git a/pkg/vm/lib/target/dart_runner.dart b/pkg/vm/lib/target/dart_runner.dart
index c1df052..995d484 100644
--- a/pkg/vm/lib/target/dart_runner.dart
+++ b/pkg/vm/lib/target/dart_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.
 
-// @dart=2.9
-
 import 'package:kernel/target/targets.dart';
 import 'package:vm/target/vm.dart' show VmTarget;
 
diff --git a/pkg/vm/lib/target/flutter.dart b/pkg/vm/lib/target/flutter.dart
index 3ffdc12..1eadf20 100644
--- a/pkg/vm/lib/target/flutter.dart
+++ b/pkg/vm/lib/target/flutter.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.
 
-// @dart=2.9
-
 import 'package:kernel/ast.dart' show Component, Library;
 import 'package:kernel/core_types.dart' show CoreTypes;
 import 'package:kernel/target/changed_structure_notifier.dart';
@@ -14,7 +12,7 @@
 class FlutterTarget extends VmTarget {
   FlutterTarget(TargetFlags flags) : super(flags);
 
-  WidgetCreatorTracker _widgetTracker;
+  late final WidgetCreatorTracker _widgetTracker = WidgetCreatorTracker();
 
   @override
   String get name => 'flutter';
@@ -57,15 +55,12 @@
       CoreTypes coreTypes,
       List<Library> libraries,
       DiagnosticReporter diagnosticReporter,
-      {void Function(String msg) logger,
-      ChangedStructureNotifier changedStructureNotifier}) {
+      {void Function(String msg)? logger,
+      ChangedStructureNotifier? changedStructureNotifier}) {
     super.performPreConstantEvaluationTransformations(
         component, coreTypes, libraries, diagnosticReporter,
         logger: logger, changedStructureNotifier: changedStructureNotifier);
     if (flags.trackWidgetCreation) {
-      if (_widgetTracker == null) {
-        _widgetTracker = WidgetCreatorTracker();
-      }
       _widgetTracker.transform(component, libraries, changedStructureNotifier);
     }
   }
diff --git a/pkg/vm/lib/target/flutter_runner.dart b/pkg/vm/lib/target/flutter_runner.dart
index a9c41ac..addd766 100644
--- a/pkg/vm/lib/target/flutter_runner.dart
+++ b/pkg/vm/lib/target/flutter_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.
 
-// @dart=2.9
-
 import 'package:kernel/target/targets.dart';
 import 'package:vm/target/vm.dart' show VmTarget;
 
diff --git a/pkg/vm/lib/target/install.dart b/pkg/vm/lib/target/install.dart
index d691d28..b22d469 100644
--- a/pkg/vm/lib/target/install.dart
+++ b/pkg/vm/lib/target/install.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.
 
-// @dart=2.9
-
 import 'package:kernel/target/targets.dart' show targets, TargetFlags;
 import 'package:vm/target/dart_runner.dart' show DartRunnerTarget;
 import 'package:vm/target/flutter.dart' show FlutterTarget;
diff --git a/pkg/vm/lib/target/vm.dart b/pkg/vm/lib/target/vm.dart
index 20cd144..ec6e1b1 100644
--- a/pkg/vm/lib/target/vm.dart
+++ b/pkg/vm/lib/target/vm.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.
 
-// @dart=2.9
-
 import 'package:kernel/ast.dart';
 import 'package:kernel/clone.dart';
 import 'package:kernel/class_hierarchy.dart';
@@ -34,14 +32,14 @@
 class VmTarget extends Target {
   final TargetFlags flags;
 
-  Class _growableList;
-  Class _immutableList;
-  Class _internalLinkedHashMap;
-  Class _immutableMap;
-  Class _oneByteString;
-  Class _twoByteString;
-  Class _smi;
-  Class _double; // _Double, not double.
+  Class? _growableList;
+  Class? _immutableList;
+  Class? _internalLinkedHashMap;
+  Class? _immutableMap;
+  Class? _oneByteString;
+  Class? _twoByteString;
+  Class? _smi;
+  Class? _double; // _Double, not double.
 
   VmTarget(this.flags);
 
@@ -116,7 +114,7 @@
     final Field little =
         coreTypes.index.getField('dart:typed_data', 'Endian', 'little');
     host.isConst = true;
-    host.initializer = new CloneVisitorNotMembers().clone(little.initializer)
+    host.initializer = new CloneVisitorNotMembers().clone(little.initializer!)
       ..parent = host;
   }
 
@@ -126,8 +124,8 @@
       CoreTypes coreTypes,
       List<Library> libraries,
       DiagnosticReporter diagnosticReporter,
-      {void Function(String msg) logger,
-      ChangedStructureNotifier changedStructureNotifier}) {
+      {void Function(String msg)? logger,
+      ChangedStructureNotifier? changedStructureNotifier}) {
     super.performPreConstantEvaluationTransformations(
         component, coreTypes, libraries, diagnosticReporter,
         logger: logger, changedStructureNotifier: changedStructureNotifier);
@@ -152,11 +150,11 @@
       CoreTypes coreTypes,
       ClassHierarchy hierarchy,
       List<Library> libraries,
-      Map<String, String> environmentDefines,
+      Map<String, String>? environmentDefines,
       DiagnosticReporter diagnosticReporter,
-      ReferenceFromIndex referenceFromIndex,
-      {void Function(String msg) logger,
-      ChangedStructureNotifier changedStructureNotifier}) {
+      ReferenceFromIndex? referenceFromIndex,
+      {void Function(String msg)? logger,
+      ChangedStructureNotifier? changedStructureNotifier}) {
     transformMixins.transformLibraries(
         this, coreTypes, hierarchy, libraries, referenceFromIndex);
     logger?.call("Transformed mixin applications");
@@ -184,7 +182,7 @@
     }
 
     // TODO(kmillikin): Make this run on a per-method basis.
-    bool productMode = environmentDefines["dart.vm.product"] == "true";
+    bool productMode = environmentDefines!["dart.vm.product"] == "true";
     transformAsync.transformLibraries(
         new TypeEnvironment(coreTypes, hierarchy), libraries,
         productMode: productMode);
@@ -204,9 +202,9 @@
       CoreTypes coreTypes,
       ClassHierarchy hierarchy,
       Procedure procedure,
-      Map<String, String> environmentDefines,
-      {void Function(String msg) logger}) {
-    bool productMode = environmentDefines["dart.vm.product"] == "true";
+      Map<String, String>? environmentDefines,
+      {void Function(String msg)? logger}) {
+    bool productMode = environmentDefines!["dart.vm.product"] == "true";
     transformAsync.transformProcedure(
         new TypeEnvironment(coreTypes, hierarchy), procedure,
         productMode: productMode);
@@ -451,7 +449,7 @@
   }
 
   @override
-  Class concreteIntLiteralClass(CoreTypes coreTypes, int value) {
+  Class? concreteIntLiteralClass(CoreTypes coreTypes, int value) {
     const int bitsPerInt32 = 32;
     const int smiBits32 = bitsPerInt32 - 2;
     const int smiMin32 = -(1 << smiBits32);
@@ -490,7 +488,6 @@
   Map<String, String> updateEnvironmentDefines(Map<String, String> map) {
     // TODO(alexmarkov): Call this from the front-end in order to have
     //  the same defines when compiling platform.
-    assert(map != null);
     map['dart.isVM'] = 'true';
     // TODO(dartbug.com/36460): Derive dart.library.* definitions from platform.
     for (String library in extraRequiredLibraries) {
diff --git a/pkg/vm/test/common_test_utils.dart b/pkg/vm/test/common_test_utils.dart
index 3f8bf9c..1ff586a 100644
--- a/pkg/vm/test/common_test_utils.dart
+++ b/pkg/vm/test/common_test_utils.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.
 
-// @dart=2.9
-
 import 'dart:async';
 import 'dart:io';
 
@@ -37,11 +35,11 @@
 }
 
 Future<Component> compileTestCaseToKernelProgram(Uri sourceUri,
-    {Target target,
+    {Target? target,
     bool enableSuperMixins = false,
-    List<String> experimentalFlags,
-    Map<String, String> environmentDefines,
-    Uri packagesFileUri}) async {
+    List<String>? experimentalFlags,
+    Map<String, String>? environmentDefines,
+    Uri? packagesFileUri}) async {
   final platformKernel =
       computePlatformBinariesLocation().resolve('vm_platform_strong.dill');
   target ??= new TestingVmTarget(new TargetFlags())
@@ -62,11 +60,11 @@
     };
 
   final Component component =
-      (await kernelForProgram(sourceUri, options)).component;
+      (await kernelForProgram(sourceUri, options))!.component!;
 
   // Make sure the library name is the same and does not depend on the order
   // of test cases.
-  component.mainMethod.enclosingLibrary.name = '#lib';
+  component.mainMethod!.enclosingLibrary.name = '#lib';
 
   return component;
 }
@@ -75,19 +73,19 @@
   final StringBuffer buffer = new StringBuffer();
   final printer = new Printer(buffer, showMetadata: true);
   printer.writeLibraryFile(library);
-  printer.writeConstantTable(library.enclosingComponent);
+  printer.writeConstantTable(library.enclosingComponent!);
   return buffer
       .toString()
-      .replaceAll(library.importUri.toString(), library.name);
+      .replaceAll(library.importUri.toString(), library.name!);
 }
 
 String kernelComponentToString(Component component) {
   final StringBuffer buffer = new StringBuffer();
   new Printer(buffer, showMetadata: true).writeComponentFile(component);
-  final mainLibrary = component.mainMethod.enclosingLibrary;
+  final mainLibrary = component.mainMethod!.enclosingLibrary;
   return buffer
       .toString()
-      .replaceAll(mainLibrary.importUri.toString(), mainLibrary.name);
+      .replaceAll(mainLibrary.importUri.toString(), mainLibrary.name!);
 }
 
 class DevNullSink<T> extends Sink<T> {