Add firefox support.

lib/src/backend/test_platform.dart

Index: lib/src/backend/test_platform.dart
diff --git a/lib/src/backend/test_platform.dart b/lib/src/backend/test_platform.dart
index a2c9b262d3627f91619012cd3c212544eb44239d..1a6599a4badc3a76ee0ad0915ccec49fa33f6310 100644
--- a/lib/src/backend/test_platform.dart
+++ b/lib/src/backend/test_platform.dart
@@ -17,8 +17,12 @@ class TestPlatform {
   static const chrome = const TestPlatform._("Chrome", "chrome",
       isBrowser: true, isJS: true, isBlink: true);
 
+  /// Mozilla Firefox.
+  static const firefox = const TestPlatform._("Firefox", "firefox",

[kevmoo, 2015/04/09 22:10:01]

Per the discussion on pkg/path: add types to this and other constants

[nweiz, 2015/04/09 22:24:55]

Done.

+      isBrowser: true, isJS: true);
+
   /// A list of all instances of [TestPlatform].
-  static const all = const [vm, chrome];
+  static const all = const [vm, chrome, firefox];
 
   /// Finds a platform by its identifier string.
   ///