Adding supported checks to media events

sdk/lib/html/dartium/html_dartium.dart

Index: sdk/lib/html/dartium/html_dartium.dart
diff --git a/sdk/lib/html/dartium/html_dartium.dart b/sdk/lib/html/dartium/html_dartium.dart
index fff74cc325a7550d88d63b927119794220e4bc14..d01751179e54dc7ea0876b06f2797c482802acc5 100644
--- a/sdk/lib/html/dartium/html_dartium.dart
+++ b/sdk/lib/html/dartium/html_dartium.dart
@@ -10812,6 +10812,18 @@ class Event extends NativeFieldWrapperClass1 {
   @DomName('Event.stopPropagation')
   void stopPropagation() native "Event_stopPropagation_Callback";
 
+
+  /**
+   * Checks to see if the event class is supported by the current platform.
+   */
+  static bool _isTypeSupported(String eventType) {
+    // Browsers throw for unsupported event names.
+    try {
+      var e = document.$dom_createEvent(eventType);
+      return e is Event;
+    } catch (_) { }
+    return false;
+  }
 }
 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
@@ -17187,6 +17199,9 @@ class MediaStreamEvents extends Events {
 class MediaStreamEvent extends Event {
   MediaStreamEvent.internal() : super.internal();
 
+  /// Checks if this type is supported on the current platform.
+  static bool get supported => true;
+
   @DocsEditable
   @DomName('MediaStreamEvent.stream')
   MediaStream get stream native "MediaStreamEvent_stream_Getter";
@@ -17303,6 +17318,9 @@ class MediaStreamTrackEvents extends Events {
 class MediaStreamTrackEvent extends Event {
   MediaStreamTrackEvent.internal() : super.internal();
 
+  /// Checks if this type is supported on the current platform.
+  static bool get supported => true;
+
   @DocsEditable
   @DomName('MediaStreamTrackEvent.track')
   MediaStreamTrack get track native "MediaStreamTrackEvent_track_Getter";