Create enum for scheduler service extension names so they can be accessed from tooling (#111222)

* Create enum for scheduler service extension names so they can be accessed from tooling

* fix two more strings

packages/flutter/lib/scheduler.dart

@@ -16,4 +16,5 @@ library scheduler;
 export 'src/scheduler/binding.dart';
 export 'src/scheduler/debug.dart';
 export 'src/scheduler/priority.dart';
+export 'src/scheduler/service_extensions.dart';
 export 'src/scheduler/ticker.dart';

packages/flutter/lib/src/scheduler/binding.dart

@@ -12,6 +12,7 @@ import 'package:flutter/foundation.dart';
 
 import 'debug.dart';
 import 'priority.dart';
+import 'service_extensions.dart';
 
 export 'dart:developer' show Flow;
 export 'dart:ui' show AppLifecycleState, FrameTiming, TimingsCallback;
@@ -355,7 +356,7 @@ mixin SchedulerBinding on BindingBase {
 
     if (!kReleaseMode) {
       registerNumericServiceExtension(
-        name: 'timeDilation',
+        name: SchedulerServiceExtensions.timeDilation.name,
         getter: () async => timeDilation,
         setter: (double value) async {
           timeDilation = value;

packages/flutter/lib/src/scheduler/service_extensions.dart

+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/// Service extension constants for the scheduler library.
+///
+/// These constants will be used when registering service extensions in the
+/// framework, and they will also be used by tools and services that call these
+/// service extensions.
+///
+/// The String value for each of these extension names should be accessed by
+/// calling the `.name` property on the enum value.
+enum SchedulerServiceExtensions {
+  /// Name of service extension that, when called, will change the value of
+  /// [timeDilation], which determines the factor by which to slow down
+  /// animations for help in development.
+  ///
+  /// See also:
+  ///
+  /// * [timeDilation], which is the field that this service extension exposes.
+  /// * [SchedulerBinding.initServiceExtensions], where the service extension is
+  ///   registered.
+  timeDilation,
+}

packages/flutter/test/foundation/service_extensions_test.dart

@@ -894,30 +894,30 @@ void main() {
 
     expect(binding.frameScheduled, isFalse);
     expect(timeDilation, 1.0);
-    result = await binding.testExtension('timeDilation', <String, String>{});
-    expect(result, <String, String>{'timeDilation': 1.0.toString()});
+    result = await binding.testExtension(SchedulerServiceExtensions.timeDilation.name, <String, String>{});
+    expect(result, <String, String>{SchedulerServiceExtensions.timeDilation.name: 1.0.toString()});
     expect(timeDilation, 1.0);
     expect(extensionChangedEvents, isEmpty);
-    result = await binding.testExtension('timeDilation', <String, String>{'timeDilation': '100.0'});
-    expect(result, <String, String>{'timeDilation': 100.0.toString()});
+    result = await binding.testExtension(SchedulerServiceExtensions.timeDilation.name, <String, String>{SchedulerServiceExtensions.timeDilation.name: '100.0'});
+    expect(result, <String, String>{SchedulerServiceExtensions.timeDilation.name: 100.0.toString()});
     expect(timeDilation, 100.0);
     expect(extensionChangedEvents.length, 1);
     extensionChangedEvent = extensionChangedEvents.last;
-    expect(extensionChangedEvent['extension'], 'ext.flutter.timeDilation');
+    expect(extensionChangedEvent['extension'], 'ext.flutter.${SchedulerServiceExtensions.timeDilation.name}');
     expect(extensionChangedEvent['value'], 100.0.toString());
-    result = await binding.testExtension('timeDilation', <String, String>{});
-    expect(result, <String, String>{'timeDilation': 100.0.toString()});
+    result = await binding.testExtension(SchedulerServiceExtensions.timeDilation.name, <String, String>{});
+    expect(result, <String, String>{SchedulerServiceExtensions.timeDilation.name: 100.0.toString()});
     expect(timeDilation, 100.0);
     expect(extensionChangedEvents.length, 1);
-    result = await binding.testExtension('timeDilation', <String, String>{'timeDilation': '1.0'});
-    expect(result, <String, String>{'timeDilation': 1.0.toString()});
+    result = await binding.testExtension(SchedulerServiceExtensions.timeDilation.name, <String, String>{SchedulerServiceExtensions.timeDilation.name: '1.0'});
+    expect(result, <String, String>{SchedulerServiceExtensions.timeDilation.name: 1.0.toString()});
     expect(timeDilation, 1.0);
     expect(extensionChangedEvents.length, 2);
     extensionChangedEvent = extensionChangedEvents.last;
-    expect(extensionChangedEvent['extension'], 'ext.flutter.timeDilation');
+    expect(extensionChangedEvent['extension'], 'ext.flutter.${SchedulerServiceExtensions.timeDilation.name}');
     expect(extensionChangedEvent['value'], 1.0.toString());
-    result = await binding.testExtension('timeDilation', <String, String>{});
-    expect(result, <String, String>{'timeDilation': 1.0.toString()});
+    result = await binding.testExtension(SchedulerServiceExtensions.timeDilation.name, <String, String>{});
+    expect(result, <String, String>{SchedulerServiceExtensions.timeDilation.name: 1.0.toString()});
     expect(timeDilation, 1.0);
     expect(extensionChangedEvents.length, 2);
     expect(binding.frameScheduled, isFalse);