Add MediaSource.supported, annotations for supported browsers, and a minimal test

tools/dom/scripts/systemhtml.py

 #!/usr/bin/python
 # 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.
 
 """This module provides shared functionality for the system to generate
 Dart:html APIs from the IDL database."""
 
 import emitter
 import logging
@@ skipping 403 matching lines @@
     'Database': "JS('bool', '!!(window.openDatabase)')",
     'DOMPoint': "JS('bool', '!!(window.DOMPoint) || !!(window.WebKitPoint)')",
     'ApplicationCache': "JS('bool', '!!(window.applicationCache)')",
     'DOMFileSystem': "JS('bool', '!!(window.webkitRequestFileSystem)')",
     'FormData': "JS('bool', '!!(window.FormData)')",
     'HashChangeEvent': "Device.isEventTypeSupported('HashChangeEvent')",
     'HTMLShadowElement': ElemSupportStr('shadow'),
     'HTMLTemplateElement': ElemSupportStr('template'),
     'MediaStreamEvent': "Device.isEventTypeSupported('MediaStreamEvent')",
     'MediaStreamTrackEvent': "Device.isEventTypeSupported('MediaStreamTrackEvent')",
+    'MediaSource': "JS('bool', '!!(window.MediaSource)')",
     'NotificationCenter': "JS('bool', '!!(window.webkitNotifications)')",
     'Performance': "JS('bool', '!!(window.performance)')",
     'SpeechRecognition': "JS('bool', '!!(window.SpeechRecognition || "
         "window.webkitSpeechRecognition)')",
     'SVGExternalResourcesRequired': ('supported(SvgElement element)',
         "JS('bool', '#.externalResourcesRequired !== undefined && "
         "#.externalResourcesRequired.animVal !== undefined', "
         "element, element)"),
     'SVGLangSpace': ('supported(SvgElement element)',
         "JS('bool', '#.xmlspace !== undefined && #.xmllang !== undefined', "
@@ skipping 840 matching lines @@
 
   def AddFile(self, basename, library_name, path):
     self._libraries[library_name].AddFile(path)
 
   def AddTypeEntry(self, library_name, idl_name, dart_name):
     self._libraries[library_name].AddTypeEntry(idl_name, dart_name)
 
   def Emit(self, emitter, auxiliary_dir):
     for lib in self._libraries.values():
       lib.Emit(emitter, auxiliary_dir)