Add firefox support.

lib/src/backend/test_platform.dart

 // Copyright (c) 2015, 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.
 
 library test.backend.test_platform;
 
 // TODO(nweiz): support pluggable platforms.
 /// An enum of all platforms on which tests can run.
 class TestPlatform {
   // When adding new platforms, be sure to update the baseline and derived
   // variable tests in test/backend/platform_selector/evaluate_test.
 
   /// The command-line Dart VM.
-  static const vm = const TestPlatform._("VM", "vm", isDartVm: true);
+  static const TestPlatform vm =
+      const TestPlatform._("VM", "vm", isDartVm: true);
 
   /// Google Chrome.
-  static const chrome = const TestPlatform._("Chrome", "chrome",
+  static const TestPlatform chrome = const TestPlatform._("Chrome", "chrome",
       isBrowser: true, isJS: true, isBlink: true);
 
+  /// Mozilla Firefox.
+  static const TestPlatform firefox = const TestPlatform._("Firefox", "firefox",
+      isBrowser: true, isJS: true);
+
   /// A list of all instances of [TestPlatform].
-  static const all = const [vm, chrome];
+  static const List<TestPlatform> all = const [vm, chrome, firefox];
 
   /// Finds a platform by its identifier string.
   ///
   /// If no platform is found, returns `null`.
   static TestPlatform find(String identifier) =>
       all.firstWhere((platform) => platform.identifier == identifier,
           orElse: () => null);
 
   /// The human-friendly name of the platform.
   final String name;
@@ skipping 11 matching lines @@
   final bool isJS;
 
   /// Whether this platform uses the Blink rendering engine.
   final bool isBlink;
 
   const TestPlatform._(this.name, this.identifier, {this.isDartVm: false,
       this.isBrowser: false, this.isJS: false, this.isBlink: false});
 
   String toString() => name;
 }