Adding supported checks to media events

tools/dom/templates/html/impl/impl_Event.darttemplate

Index: tools/dom/templates/html/impl/impl_Event.darttemplate
diff --git a/tools/dom/templates/html/impl/impl_Event.darttemplate b/tools/dom/templates/html/impl/impl_Event.darttemplate
index 9fddd1c56b5a5d99b7f5bc8c4f02cb4f6178b5d8..b982e0143509e3351d6b3ca471c99145773a1c4e 100644
--- a/tools/dom/templates/html/impl/impl_Event.darttemplate
+++ b/tools/dom/templates/html/impl/impl_Event.darttemplate
@@ -16,4 +16,16 @@ $(ANNOTATIONS)class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
   factory $CLASSNAME(String type, [bool canBubble = true, bool cancelable = true]) =>
       _$(CLASSNAME)FactoryProvider.create$CLASSNAME(type, canBubble, cancelable);
 $!MEMBERS
+
+  /**
+   * Checks to see if the event class is supported by the current platform.
+   */
+  static bool _isTypeSupported(String eventType) {
+    // Browsers throw for unsupported event names.
+    try {
+      var e = document.$dom_createEvent(eventType);
+      return e is Event;
+    } catch (_) { }
+    return false;
+  }
 }