Make html metadata follow the spec.

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

 // 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
 // BSD-style license that can be found in the LICENSE file.
 
 part of $LIBRARYNAME;
 
 $(ANNOTATIONS)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
 
 $if DART2JS
   @DomName('Navigator.language')
@@ skipping 31 matching lines @@
    *                 'optional':
    *                    [{ 'minFrameRate': 60 },
    *                     { 'maxWidth': 640 }]
    *     });
    *
    * See also:
    * * [MediaStream.supported]
    */
   @DomName('Navigator.webkitGetUserMedia')
   @SupportedBrowser(SupportedBrowser.CHROME)
-  @Experimental
+  @Experimental()
   Future<MediaStream> getUserMedia({audio: false, video: false}) {
     var completer = new Completer<MediaStream>();
     var options = {
       'audio': audio,
       'video': video
     };
 $if DART2JS
     _ensureGetUserMedia();
     this._getUserMedia(convertDartToNative_SerializedScriptValue(options),
       (stream) {
@@ skipping 23 matching lines @@
     }
   }
 
   @JSName('getUserMedia')
   void _getUserMedia(options, _NavigatorUserMediaSuccessCallback success,
       _NavigatorUserMediaErrorCallback error) native;
 $endif
 
 $!MEMBERS
 }