refactor context to be implicit-downcast safe (#31622)

diff --git a/packages/flutter_tools/lib/src/android/android_sdk.dart b/packages/flutter_tools/lib/src/android/android_sdk.dart
index d8a7326..65f40aa 100644
--- a/packages/flutter_tools/lib/src/android/android_sdk.dart
+++ b/packages/flutter_tools/lib/src/android/android_sdk.dart

@@ -17,7 +17,7 @@
 import '../globals.dart';
 import 'android_studio.dart' as android_studio;
 
-AndroidSdk get androidSdk => context[AndroidSdk];
+AndroidSdk get androidSdk => context.get<AndroidSdk>();
 
 const String kAndroidHome = 'ANDROID_HOME';
 const String kAndroidSdkRoot = 'ANDROID_SDK_ROOT';

diff --git a/packages/flutter_tools/lib/src/android/android_studio.dart b/packages/flutter_tools/lib/src/android/android_studio.dart
index 8457d26..f1330dd 100644
--- a/packages/flutter_tools/lib/src/android/android_studio.dart
+++ b/packages/flutter_tools/lib/src/android/android_studio.dart

@@ -13,7 +13,7 @@
 import '../ios/ios_workflow.dart';
 import '../ios/plist_utils.dart' as plist;
 
-AndroidStudio get androidStudio => context[AndroidStudio];
+AndroidStudio get androidStudio => context.get<AndroidStudio>();
 
 // Android Studio layout:
 

diff --git a/packages/flutter_tools/lib/src/android/android_workflow.dart b/packages/flutter_tools/lib/src/android/android_workflow.dart
index 5da192c..780e382 100644
--- a/packages/flutter_tools/lib/src/android/android_workflow.dart
+++ b/packages/flutter_tools/lib/src/android/android_workflow.dart

@@ -21,9 +21,9 @@
 const int kAndroidSdkMinVersion = 28;
 final Version kAndroidSdkBuildToolsMinVersion = Version(28, 0, 3);
 
-AndroidWorkflow get androidWorkflow => context[AndroidWorkflow];
-AndroidValidator get androidValidator => context[AndroidValidator];
-AndroidLicenseValidator get androidLicenseValidator => context[AndroidLicenseValidator];
+AndroidWorkflow get androidWorkflow => context.get<AndroidWorkflow>();
+AndroidValidator get androidValidator => context.get<AndroidValidator>();
+AndroidLicenseValidator get androidLicenseValidator => context.get<AndroidLicenseValidator>();
 
 enum LicensesAccepted {
   none,

diff --git a/packages/flutter_tools/lib/src/application_package.dart b/packages/flutter_tools/lib/src/application_package.dart
index c40a771..2f83860 100644
--- a/packages/flutter_tools/lib/src/application_package.dart
+++ b/packages/flutter_tools/lib/src/application_package.dart

@@ -28,7 +28,7 @@
 import 'windows/application_package.dart';
 
 class ApplicationPackageFactory {
-  static ApplicationPackageFactory get instance => context[ApplicationPackageFactory];
+  static ApplicationPackageFactory get instance => context.get<ApplicationPackageFactory>();
 
   Future<ApplicationPackage> getPackageForPlatform(
     TargetPlatform platform, {

diff --git a/packages/flutter_tools/lib/src/artifacts.dart b/packages/flutter_tools/lib/src/artifacts.dart
index b2080eb..8dae706 100644
--- a/packages/flutter_tools/lib/src/artifacts.dart
+++ b/packages/flutter_tools/lib/src/artifacts.dart

@@ -100,7 +100,7 @@
 
 // Manages the engine artifacts of Flutter.
 abstract class Artifacts {
-  static Artifacts get instance => context[Artifacts];
+  static Artifacts get instance => context.get<Artifacts>();
 
   static LocalEngineArtifacts getLocalEngine(String engineSrcPath, EngineBuildPaths engineBuildPaths) {
     return LocalEngineArtifacts(engineSrcPath, engineBuildPaths.targetEngine, engineBuildPaths.hostEngine);

diff --git a/packages/flutter_tools/lib/src/asset.dart b/packages/flutter_tools/lib/src/asset.dart
index e1e16e4..498505c 100644
--- a/packages/flutter_tools/lib/src/asset.dart
+++ b/packages/flutter_tools/lib/src/asset.dart

@@ -23,7 +23,7 @@
 /// Injected factory class for spawning [AssetBundle] instances.
 abstract class AssetBundleFactory {
   /// The singleton instance, pulled from the [AppContext].
-  static AssetBundleFactory get instance => context[AssetBundleFactory];
+  static AssetBundleFactory get instance => context.get<AssetBundleFactory>();
 
   static AssetBundleFactory get defaultInstance => _kManifestFactory;
 

diff --git a/packages/flutter_tools/lib/src/base/build.dart b/packages/flutter_tools/lib/src/base/build.dart
index 3e9cad6..e2bf600 100644
--- a/packages/flutter_tools/lib/src/base/build.dart
+++ b/packages/flutter_tools/lib/src/base/build.dart

@@ -21,7 +21,7 @@
 import 'fingerprint.dart';
 import 'process.dart';
 
-GenSnapshot get genSnapshot => context[GenSnapshot];
+GenSnapshot get genSnapshot => context.get<GenSnapshot>();
 
 /// A snapshot build configuration.
 class SnapshotType {

diff --git a/packages/flutter_tools/lib/src/base/config.dart b/packages/flutter_tools/lib/src/base/config.dart
index 54c440c..388e989 100644
--- a/packages/flutter_tools/lib/src/base/config.dart
+++ b/packages/flutter_tools/lib/src/base/config.dart

@@ -14,7 +14,7 @@
       _values = json.decode(_configFile.readAsStringSync());
   }
 
-  static Config get instance => context[Config];
+  static Config get instance => context.get<Config>();
 
   File _configFile;
   String get configPath => _configFile.path;

diff --git a/packages/flutter_tools/lib/src/base/context.dart b/packages/flutter_tools/lib/src/base/context.dart
index 5bc60d5..84fc8fc 100644
--- a/packages/flutter_tools/lib/src/base/context.dart
+++ b/packages/flutter_tools/lib/src/base/context.dart

@@ -33,7 +33,7 @@
 /// context will not have any values associated with it.
 ///
 /// This is guaranteed to never return `null`.
-AppContext get context => Zone.current[_Key.key] ?? AppContext._root;
+AppContext get context => Zone.current[_Key.key] as AppContext ?? AppContext._root;
 
 /// A lookup table (mapping types to values) and an implied scope, in which
 /// code is run.
@@ -107,6 +107,17 @@
 
   /// Gets the value associated with the specified [type], or `null` if no
   /// such value has been associated.
+  T get<T>() {
+    dynamic value = _generateIfNecessary(T, _overrides);
+    if (value == null && _parent != null) {
+      value = _parent.get<T>();
+    }
+    return _unboxNull(value ?? _generateIfNecessary(T, _fallbacks)) as T;
+  }
+
+  /// Gets the value associated with the specified [type], or `null` if no
+  /// such value has been associated.
+  @Deprecated('use get<T> instead for type safety.')
   Object operator [](Type type) {
     dynamic value = _generateIfNecessary(type, _overrides);
     if (value == null && _parent != null)

diff --git a/packages/flutter_tools/lib/src/base/file_system.dart b/packages/flutter_tools/lib/src/base/file_system.dart
index 5bb23ab..94de99c 100644
--- a/packages/flutter_tools/lib/src/base/file_system.dart
+++ b/packages/flutter_tools/lib/src/base/file_system.dart

@@ -23,7 +23,7 @@
 ///
 /// By default it uses local disk-based implementation. Override this in tests
 /// with [MemoryFileSystem].
-FileSystem get fs => context[FileSystem] ?? _kLocalFs;
+FileSystem get fs => context.get<FileSystem>() ?? _kLocalFs;
 
 /// Gets a [FileSystem] that will record file system activity to the specified
 /// base recording [location].

diff --git a/packages/flutter_tools/lib/src/base/flags.dart b/packages/flutter_tools/lib/src/base/flags.dart
index 81442a9..b4e3ab1 100644
--- a/packages/flutter_tools/lib/src/base/flags.dart
+++ b/packages/flutter_tools/lib/src/base/flags.dart

@@ -8,7 +8,7 @@
 
 /// command-line flags and options that were specified during the invocation of
 /// the Flutter tool.
-Flags get flags => context[Flags];
+Flags get flags => context.get<Flags>();
 
 /// Encapsulation of the command-line flags and options that were specified
 /// during the invocation of the Flutter tool.

diff --git a/packages/flutter_tools/lib/src/base/io.dart b/packages/flutter_tools/lib/src/base/io.dart
index 1c9761e..4c9d225 100644
--- a/packages/flutter_tools/lib/src/base/io.dart
+++ b/packages/flutter_tools/lib/src/base/io.dart

@@ -163,7 +163,7 @@
   bool get supportsAnsiEscapes => hasTerminal ? io.stdout.supportsAnsiEscapes : false;
 }
 
-Stdio get stdio => context[Stdio];
+Stdio get stdio => context.get<Stdio>();
 io.IOSink get stdout => stdio.stdout;
 Stream<List<int>> get stdin => stdio.stdin;
 io.IOSink get stderr => stdio.stderr;

diff --git a/packages/flutter_tools/lib/src/base/logger.dart b/packages/flutter_tools/lib/src/base/logger.dart
index b1402d2..e9e508b 100644
--- a/packages/flutter_tools/lib/src/base/logger.dart
+++ b/packages/flutter_tools/lib/src/base/logger.dart

@@ -19,7 +19,7 @@
 /// The [TimeoutConfiguration] instance.
 ///
 /// If not provided via injection, a default instance is provided.
-TimeoutConfiguration get timeoutConfiguration => context[TimeoutConfiguration] ?? const TimeoutConfiguration();
+TimeoutConfiguration get timeoutConfiguration => context.get<TimeoutConfiguration>() ?? const TimeoutConfiguration();
 
 class TimeoutConfiguration {
   const TimeoutConfiguration();
@@ -486,7 +486,7 @@
   final VoidCallback onFinish;
 
   @protected
-  final Stopwatch _stopwatch = context[Stopwatch] ?? Stopwatch();
+  final Stopwatch _stopwatch = context.get<Stopwatch>() ?? Stopwatch();
 
   @protected
   @visibleForTesting

diff --git a/packages/flutter_tools/lib/src/base/net.dart b/packages/flutter_tools/lib/src/base/net.dart
index 742bd8b..f139c9d 100644
--- a/packages/flutter_tools/lib/src/base/net.dart
+++ b/packages/flutter_tools/lib/src/base/net.dart

@@ -36,8 +36,8 @@
 Future<List<int>> _attempt(Uri url, { bool onlyHeaders = false }) async {
   printTrace('Downloading: $url');
   HttpClient httpClient;
-  if (context[HttpClientFactory] != null) {
-    httpClient = (context[HttpClientFactory] as HttpClientFactory)(); // ignore: avoid_as
+  if (context.get<HttpClientFactory>() != null) {
+    httpClient = context.get<HttpClientFactory>()();
   } else {
     httpClient = HttpClient();
   }

diff --git a/packages/flutter_tools/lib/src/base/os.dart b/packages/flutter_tools/lib/src/base/os.dart
index dd75337..30c832e 100644
--- a/packages/flutter_tools/lib/src/base/os.dart
+++ b/packages/flutter_tools/lib/src/base/os.dart

@@ -11,7 +11,7 @@
 import 'process_manager.dart';
 
 /// Returns [OperatingSystemUtils] active in the current app context (i.e. zone).
-OperatingSystemUtils get os => context[OperatingSystemUtils];
+OperatingSystemUtils get os => context.get<OperatingSystemUtils>();
 
 abstract class OperatingSystemUtils {
   factory OperatingSystemUtils() {

diff --git a/packages/flutter_tools/lib/src/base/platform.dart b/packages/flutter_tools/lib/src/base/platform.dart
index 359cc5f..9ab824d 100644
--- a/packages/flutter_tools/lib/src/base/platform.dart
+++ b/packages/flutter_tools/lib/src/base/platform.dart

@@ -14,7 +14,7 @@
 const Platform _kLocalPlatform = LocalPlatform();
 const String _kRecordingType = 'platform';
 
-Platform get platform => context[Platform] ?? _kLocalPlatform;
+Platform get platform => context.get<Platform>() ?? _kLocalPlatform;
 
 /// Serializes the current [platform] to the specified base recording
 /// [location].

diff --git a/packages/flutter_tools/lib/src/base/process_manager.dart b/packages/flutter_tools/lib/src/base/process_manager.dart
index cbf8661..5929ef9 100644
--- a/packages/flutter_tools/lib/src/base/process_manager.dart
+++ b/packages/flutter_tools/lib/src/base/process_manager.dart

@@ -16,7 +16,7 @@
 const ProcessManager _kLocalProcessManager = LocalProcessManager();
 
 /// The active process manager.
-ProcessManager get processManager => context[ProcessManager] ?? _kLocalProcessManager;
+ProcessManager get processManager => context.get<ProcessManager>() ?? _kLocalProcessManager;
 
 /// Gets a [ProcessManager] that will record process invocation activity to the
 /// specified base recording [location].

diff --git a/packages/flutter_tools/lib/src/base/terminal.dart b/packages/flutter_tools/lib/src/base/terminal.dart
index 8f9eb45..396b9a2 100644
--- a/packages/flutter_tools/lib/src/base/terminal.dart
+++ b/packages/flutter_tools/lib/src/base/terminal.dart

@@ -14,9 +14,9 @@
 final AnsiTerminal _kAnsiTerminal = AnsiTerminal();
 
 AnsiTerminal get terminal {
-  return (context == null || context[AnsiTerminal] == null)
+  return (context == null || context.get<AnsiTerminal>() == null)
       ? _kAnsiTerminal
-      : context[AnsiTerminal];
+      : context.get<AnsiTerminal>();
 }
 
 enum TerminalColor {
@@ -31,9 +31,9 @@
 
 final OutputPreferences _kOutputPreferences = OutputPreferences();
 
-OutputPreferences get outputPreferences => (context == null || context[OutputPreferences] == null)
+OutputPreferences get outputPreferences => (context == null || context.get<OutputPreferences>() == null)
     ? _kOutputPreferences
-    : context[OutputPreferences];
+    : context.get<OutputPreferences>();
 
 /// A class that contains the context settings for command text output to the
 /// console.

diff --git a/packages/flutter_tools/lib/src/base/time.dart b/packages/flutter_tools/lib/src/base/time.dart
index 5ba7e02..685fde2 100644
--- a/packages/flutter_tools/lib/src/base/time.dart
+++ b/packages/flutter_tools/lib/src/base/time.dart

@@ -5,7 +5,7 @@
 import 'context.dart';
 
 /// The current system clock instance.
-SystemClock get systemClock => context[SystemClock];
+SystemClock get systemClock => context.get<SystemClock>();
 
 /// A class for making time based operations testable.
 class SystemClock {

diff --git a/packages/flutter_tools/lib/src/base/user_messages.dart b/packages/flutter_tools/lib/src/base/user_messages.dart
index 104d364..58b83e8 100644
--- a/packages/flutter_tools/lib/src/base/user_messages.dart
+++ b/packages/flutter_tools/lib/src/base/user_messages.dart

@@ -4,7 +4,7 @@
 
 import 'context.dart';
 
-UserMessages get userMessages => context[UserMessages];
+UserMessages get userMessages => context.get<UserMessages>();
 
 /// Class containing message strings that can be produced by Flutter tools.
 class UserMessages {

diff --git a/packages/flutter_tools/lib/src/base/utils.dart b/packages/flutter_tools/lib/src/base/utils.dart
index a18ae8b..71f835e 100644
--- a/packages/flutter_tools/lib/src/base/utils.dart
+++ b/packages/flutter_tools/lib/src/base/utils.dart

@@ -49,7 +49,7 @@
 }
 
 bool get isRunningOnBot {
-  final BotDetector botDetector = context[BotDetector] ?? _kBotDetector;
+  final BotDetector botDetector = context.get<BotDetector>() ?? _kBotDetector;
   return botDetector.isRunningOnBot;
 }
 

diff --git a/packages/flutter_tools/lib/src/cache.dart b/packages/flutter_tools/lib/src/cache.dart
index db42bac..a71be8e 100644
--- a/packages/flutter_tools/lib/src/cache.dart
+++ b/packages/flutter_tools/lib/src/cache.dart

@@ -197,7 +197,7 @@
   }
   String _fuchsiaRevision;
 
-  static Cache get instance => context[Cache];
+  static Cache get instance => context.get<Cache>();
 
   /// Return the top-level directory in the cache; this is `bin/cache`.
   Directory getRoot() {

diff --git a/packages/flutter_tools/lib/src/codegen.dart b/packages/flutter_tools/lib/src/codegen.dart
index c2503a0..0993819 100644
--- a/packages/flutter_tools/lib/src/codegen.dart
+++ b/packages/flutter_tools/lib/src/codegen.dart

@@ -22,7 +22,7 @@
 ///
 /// If [experimentalBuildEnabled] is false, this will contain an unsupported
 /// implementation.
-CodeGenerator get codeGenerator => context[CodeGenerator];
+CodeGenerator get codeGenerator => context.get<CodeGenerator>();
 
 /// A wrapper for a build_runner process which delegates to a generated
 /// build script.

diff --git a/packages/flutter_tools/lib/src/compile.dart b/packages/flutter_tools/lib/src/compile.dart
index f2c15f92..3ab5dd5 100644
--- a/packages/flutter_tools/lib/src/compile.dart
+++ b/packages/flutter_tools/lib/src/compile.dart

@@ -23,7 +23,7 @@
 import 'globals.dart';
 import 'project.dart';
 
-KernelCompilerFactory get kernelCompilerFactory => context[KernelCompilerFactory];
+KernelCompilerFactory get kernelCompilerFactory => context.get<KernelCompilerFactory>();
 
 class KernelCompilerFactory {
   const KernelCompilerFactory();

diff --git a/packages/flutter_tools/lib/src/devfs.dart b/packages/flutter_tools/lib/src/devfs.dart
index 021c5b9..b040dc8 100644
--- a/packages/flutter_tools/lib/src/devfs.dart
+++ b/packages/flutter_tools/lib/src/devfs.dart

@@ -26,7 +26,7 @@
   bool noDirectorySymlinks = false;
 }
 
-DevFSConfig get devFSConfig => context[DevFSConfig];
+DevFSConfig get devFSConfig => context.get<DevFSConfig>();
 
 /// Common superclass for content copied to the device.
 abstract class DevFSContent {

diff --git a/packages/flutter_tools/lib/src/device.dart b/packages/flutter_tools/lib/src/device.dart
index 028894e..8765e54 100644
--- a/packages/flutter_tools/lib/src/device.dart
+++ b/packages/flutter_tools/lib/src/device.dart

@@ -24,7 +24,7 @@
 import 'web/web_device.dart';
 import 'windows/windows_device.dart';
 
-DeviceManager get deviceManager => context[DeviceManager];
+DeviceManager get deviceManager => context.get<DeviceManager>();
 
 /// A class to get all available devices.
 class DeviceManager {

diff --git a/packages/flutter_tools/lib/src/doctor.dart b/packages/flutter_tools/lib/src/doctor.dart
index 6c80b62..60089f0 100644
--- a/packages/flutter_tools/lib/src/doctor.dart
+++ b/packages/flutter_tools/lib/src/doctor.dart

@@ -33,11 +33,11 @@
 import 'vscode/vscode_validator.dart';
 import 'windows/windows_workflow.dart';
 
-Doctor get doctor => context[Doctor];
+Doctor get doctor => context.get<Doctor>();
 
 abstract class DoctorValidatorsProvider {
   /// The singleton instance, pulled from the [AppContext].
-  static DoctorValidatorsProvider get instance => context[DoctorValidatorsProvider];
+  static DoctorValidatorsProvider get instance => context.get<DoctorValidatorsProvider>();
 
   static final DoctorValidatorsProvider defaultInstance = _DefaultDoctorValidatorsProvider();
 

diff --git a/packages/flutter_tools/lib/src/emulator.dart b/packages/flutter_tools/lib/src/emulator.dart
index 61f0c34..96f20f8 100644
--- a/packages/flutter_tools/lib/src/emulator.dart
+++ b/packages/flutter_tools/lib/src/emulator.dart

@@ -13,7 +13,7 @@
 import 'globals.dart';
 import 'ios/ios_emulators.dart';
 
-EmulatorManager get emulatorManager => context[EmulatorManager];
+EmulatorManager get emulatorManager => context.get<EmulatorManager>();
 
 /// A class to get all available emulators.
 class EmulatorManager {

diff --git a/packages/flutter_tools/lib/src/fuchsia/fuchsia_sdk.dart b/packages/flutter_tools/lib/src/fuchsia/fuchsia_sdk.dart
index ed090c0..e97c56f 100644
--- a/packages/flutter_tools/lib/src/fuchsia/fuchsia_sdk.dart
+++ b/packages/flutter_tools/lib/src/fuchsia/fuchsia_sdk.dart

@@ -13,10 +13,10 @@
 import '../globals.dart';
 
 /// The [FuchsiaSdk] instance.
-FuchsiaSdk get fuchsiaSdk => context[FuchsiaSdk];
+FuchsiaSdk get fuchsiaSdk => context.get<FuchsiaSdk>();
 
 /// The [FuchsiaArtifacts] instance.
-FuchsiaArtifacts get fuchsiaArtifacts => context[FuchsiaArtifacts];
+FuchsiaArtifacts get fuchsiaArtifacts => context.get<FuchsiaArtifacts>();
 
 /// The Fuchsia SDK shell commands.
 ///

diff --git a/packages/flutter_tools/lib/src/fuchsia/fuchsia_workflow.dart b/packages/flutter_tools/lib/src/fuchsia/fuchsia_workflow.dart
index a0d3022..5fc5562 100644
--- a/packages/flutter_tools/lib/src/fuchsia/fuchsia_workflow.dart
+++ b/packages/flutter_tools/lib/src/fuchsia/fuchsia_workflow.dart

@@ -8,7 +8,7 @@
 import 'fuchsia_sdk.dart';
 
 /// The [FuchsiaWorkflow] instance.
-FuchsiaWorkflow get fuchsiaWorkflow => context[FuchsiaWorkflow];
+FuchsiaWorkflow get fuchsiaWorkflow => context.get<FuchsiaWorkflow>();
 
 /// The Fuchsia-specific implementation of a [Workflow].
 ///

diff --git a/packages/flutter_tools/lib/src/globals.dart b/packages/flutter_tools/lib/src/globals.dart
index 4c3f6b8..32a0051 100644
--- a/packages/flutter_tools/lib/src/globals.dart
+++ b/packages/flutter_tools/lib/src/globals.dart

@@ -9,7 +9,7 @@
 import 'base/terminal.dart';
 import 'cache.dart';
 
-Logger get logger => context[Logger];
+Logger get logger => context.get<Logger>();
 Cache get cache => Cache.instance;
 Config get config => Config.instance;
 Artifacts get artifacts => Artifacts.instance;

diff --git a/packages/flutter_tools/lib/src/ios/cocoapods.dart b/packages/flutter_tools/lib/src/ios/cocoapods.dart
index 03c89da..2837371 100644
--- a/packages/flutter_tools/lib/src/ios/cocoapods.dart
+++ b/packages/flutter_tools/lib/src/ios/cocoapods.dart

@@ -37,7 +37,7 @@
   brew upgrade cocoapods
   pod setup''';
 
-CocoaPods get cocoaPods => context[CocoaPods];
+CocoaPods get cocoaPods => context.get<CocoaPods>();
 
 /// Result of evaluating the CocoaPods installation.
 enum CocoaPodsStatus {

diff --git a/packages/flutter_tools/lib/src/ios/ios_workflow.dart b/packages/flutter_tools/lib/src/ios/ios_workflow.dart
index 224c227..c0ced36 100644
--- a/packages/flutter_tools/lib/src/ios/ios_workflow.dart
+++ b/packages/flutter_tools/lib/src/ios/ios_workflow.dart

@@ -15,9 +15,9 @@
 import 'mac.dart';
 import 'plist_utils.dart' as plist;
 
-IOSWorkflow get iosWorkflow => context[IOSWorkflow];
-IOSValidator get iosValidator => context[IOSValidator];
-CocoaPodsValidator get cocoapodsValidator => context[CocoaPodsValidator];
+IOSWorkflow get iosWorkflow => context.get<IOSWorkflow>();
+IOSValidator get iosValidator => context.get<IOSValidator>();
+CocoaPodsValidator get cocoapodsValidator => context.get<CocoaPodsValidator>();
 
 class IOSWorkflow implements Workflow {
   const IOSWorkflow();

diff --git a/packages/flutter_tools/lib/src/ios/mac.dart b/packages/flutter_tools/lib/src/ios/mac.dart
index 396d40c..81744cb 100644
--- a/packages/flutter_tools/lib/src/ios/mac.dart
+++ b/packages/flutter_tools/lib/src/ios/mac.dart

@@ -31,9 +31,9 @@
 const int kXcodeRequiredVersionMajor = 9;
 const int kXcodeRequiredVersionMinor = 0;
 
-IMobileDevice get iMobileDevice => context[IMobileDevice];
-PlistBuddy get plistBuddy => context[PlistBuddy];
-Xcode get xcode => context[Xcode];
+IMobileDevice get iMobileDevice => context.get<IMobileDevice>();
+PlistBuddy get plistBuddy => context.get<PlistBuddy>();
+Xcode get xcode => context.get<Xcode>();
 
 class PlistBuddy {
   const PlistBuddy();

diff --git a/packages/flutter_tools/lib/src/ios/simulators.dart b/packages/flutter_tools/lib/src/ios/simulators.dart
index 9573dfe..3596c6e 100644
--- a/packages/flutter_tools/lib/src/ios/simulators.dart
+++ b/packages/flutter_tools/lib/src/ios/simulators.dart

@@ -41,7 +41,7 @@
 
 class IOSSimulatorUtils {
   /// Returns [IOSSimulatorUtils] active in the current app context (i.e. zone).
-  static IOSSimulatorUtils get instance => context[IOSSimulatorUtils];
+  static IOSSimulatorUtils get instance => context.get<IOSSimulatorUtils>();
 
   List<IOSSimulator> getAttachedDevices() {
     if (!xcode.isInstalledAndMeetsVersionCheck)
@@ -56,7 +56,7 @@
 /// A wrapper around the `simctl` command line tool.
 class SimControl {
   /// Returns [SimControl] active in the current app context (i.e. zone).
-  static SimControl get instance => context[SimControl];
+  static SimControl get instance => context.get<SimControl>();
 
   /// Runs `simctl list --json` and returns the JSON of the corresponding
   /// [section].

diff --git a/packages/flutter_tools/lib/src/ios/xcodeproj.dart b/packages/flutter_tools/lib/src/ios/xcodeproj.dart
index 17a2fde..d4441df 100644
--- a/packages/flutter_tools/lib/src/ios/xcodeproj.dart
+++ b/packages/flutter_tools/lib/src/ios/xcodeproj.dart

@@ -127,7 +127,7 @@
   generatedXcodePropertiesFile.writeAsStringSync(localsBuffer.toString());
 }
 
-XcodeProjectInterpreter get xcodeProjectInterpreter => context[XcodeProjectInterpreter];
+XcodeProjectInterpreter get xcodeProjectInterpreter => context.get<XcodeProjectInterpreter>();
 
 /// Interpreter of Xcode projects.
 class XcodeProjectInterpreter {

diff --git a/packages/flutter_tools/lib/src/linux/linux_workflow.dart b/packages/flutter_tools/lib/src/linux/linux_workflow.dart
index cb60502..bf7a04d 100644
--- a/packages/flutter_tools/lib/src/linux/linux_workflow.dart
+++ b/packages/flutter_tools/lib/src/linux/linux_workflow.dart

@@ -8,7 +8,7 @@
 import '../doctor.dart';
 
 /// The [WindowsWorkflow] instance.
-LinuxWorkflow get linuxWorkflow => context[LinuxWorkflow];
+LinuxWorkflow get linuxWorkflow => context.get<LinuxWorkflow>();
 
 /// The windows-specific implementation of a [Workflow].
 ///

diff --git a/packages/flutter_tools/lib/src/macos/macos_workflow.dart b/packages/flutter_tools/lib/src/macos/macos_workflow.dart
index 6215421..bf5900b 100644
--- a/packages/flutter_tools/lib/src/macos/macos_workflow.dart
+++ b/packages/flutter_tools/lib/src/macos/macos_workflow.dart

@@ -8,7 +8,7 @@
 import '../doctor.dart';
 
 /// The [MacOSWorkflow] instance.
-MacOSWorkflow get macOSWorkflow => context[MacOSWorkflow];
+MacOSWorkflow get macOSWorkflow => context.get<MacOSWorkflow>();
 
 /// The macOS-specific implementation of a [Workflow].
 ///

diff --git a/packages/flutter_tools/lib/src/run_hot.dart b/packages/flutter_tools/lib/src/run_hot.dart
index 8a061a6..e59dcbb 100644
--- a/packages/flutter_tools/lib/src/run_hot.dart
+++ b/packages/flutter_tools/lib/src/run_hot.dart

@@ -40,7 +40,7 @@
   }
 }
 
-HotRunnerConfig get hotRunnerConfig => context[HotRunnerConfig];
+HotRunnerConfig get hotRunnerConfig => context.get<HotRunnerConfig>();
 
 const bool kHotReloadDefault = true;
 

diff --git a/packages/flutter_tools/lib/src/runner/flutter_command.dart b/packages/flutter_tools/lib/src/runner/flutter_command.dart
index 4b5706c..24da1fb 100644
--- a/packages/flutter_tools/lib/src/runner/flutter_command.dart
+++ b/packages/flutter_tools/lib/src/runner/flutter_command.dart

@@ -77,7 +77,7 @@
   /// The currently executing command (or sub-command).
   ///
   /// Will be `null` until the top-most command has begun execution.
-  static FlutterCommand get current => context[FlutterCommand];
+  static FlutterCommand get current => context.get<FlutterCommand>();
 
   /// The option name for a custom observatory port.
   static const String observatoryPortOption = 'observatory-port';

diff --git a/packages/flutter_tools/lib/src/usage.dart b/packages/flutter_tools/lib/src/usage.dart
index a570d73..1902940 100644
--- a/packages/flutter_tools/lib/src/usage.dart
+++ b/packages/flutter_tools/lib/src/usage.dart

@@ -55,7 +55,7 @@
   }
 
   /// Returns [Usage] active in the current app context.
-  static Usage get instance => context[Usage];
+  static Usage get instance => context.get<Usage>();
 
   Analytics _analytics;
 

diff --git a/packages/flutter_tools/lib/src/version.dart b/packages/flutter_tools/lib/src/version.dart
index d571f37..7bcdf3c 100644
--- a/packages/flutter_tools/lib/src/version.dart
+++ b/packages/flutter_tools/lib/src/version.dart

@@ -179,7 +179,7 @@
       await _run(<String>['git', 'remote', 'remove', _versionCheckRemote]);
   }
 
-  static FlutterVersion get instance => context[FlutterVersion];
+  static FlutterVersion get instance => context.get<FlutterVersion>();
 
   /// Return a short string for the version (e.g. `master/0.0.59-pre.92`, `scroll_refactor/a76bc8e22b`).
   String getVersionString({ bool redactUnknownBranches = false }) {

diff --git a/packages/flutter_tools/lib/src/vmservice.dart b/packages/flutter_tools/lib/src/vmservice.dart
index ff5c08f..c5616db 100644
--- a/packages/flutter_tools/lib/src/vmservice.dart
+++ b/packages/flutter_tools/lib/src/vmservice.dart

@@ -82,7 +82,7 @@
       delay *= 2;
   }
 
-  final WebSocketConnector constructor = context[WebSocketConnector] ?? io.WebSocket.connect;
+  final WebSocketConnector constructor = context.get<WebSocketConnector>() ?? io.WebSocket.connect;
   while (socket == null) {
     attempts += 1;
     try {

diff --git a/packages/flutter_tools/lib/src/web/compile.dart b/packages/flutter_tools/lib/src/web/compile.dart
index 90fc421..892b2ba 100644
--- a/packages/flutter_tools/lib/src/web/compile.dart
+++ b/packages/flutter_tools/lib/src/web/compile.dart

@@ -15,7 +15,7 @@
 import '../globals.dart';
 
 /// The [WebCompiler] instance.
-WebCompiler get webCompiler => context[WebCompiler];
+WebCompiler get webCompiler => context.get<WebCompiler>();
 
 /// A wrapper around dart2js for web compilation.
 class WebCompiler {

diff --git a/packages/flutter_tools/lib/src/web/web_device.dart b/packages/flutter_tools/lib/src/web/web_device.dart
index fd47dfa..3d3a1ba 100644
--- a/packages/flutter_tools/lib/src/web/web_device.dart
+++ b/packages/flutter_tools/lib/src/web/web_device.dart

@@ -16,7 +16,7 @@
 import '../version.dart';
 import '../web/compile.dart';
 
-ChromeLauncher get chromeLauncher => context[ChromeLauncher];
+ChromeLauncher get chromeLauncher => context.get<ChromeLauncher>();
 
 /// Only launch or display web devices if `FLUTTER_WEB`
 /// environment variable is set to true.

diff --git a/packages/flutter_tools/lib/src/windows/windows_workflow.dart b/packages/flutter_tools/lib/src/windows/windows_workflow.dart
index c5d050e..5dae426 100644
--- a/packages/flutter_tools/lib/src/windows/windows_workflow.dart
+++ b/packages/flutter_tools/lib/src/windows/windows_workflow.dart

@@ -8,7 +8,7 @@
 import '../doctor.dart';
 
 /// The [WindowsWorkflow] instance.
-WindowsWorkflow get windowsWorkflow => context[WindowsWorkflow];
+WindowsWorkflow get windowsWorkflow => context.get<WindowsWorkflow>();
 
 /// The windows-specific implementation of a [Workflow].
 ///