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

tools/dom/scripts/dartmetadata.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 to provide Dart metadata for
 DOM APIs.
 """
 
 import copy
@@ skipping 501 matching lines @@
     "@SupportedBrowser(SupportedBrowser.CHROME)",
     "@SupportedBrowser(SupportedBrowser.IE, '10')",
     "@SupportedBrowser(SupportedBrowser.SAFARI)",
   ],
   'IDBFactory': _indexed_db_annotations,
   'IDBDatabase': _indexed_db_annotations,
   'MediaStream': _rtc_annotations,
   'MediaStreamEvent': _rtc_annotations,
   'MediaStreamTrack': _rtc_annotations,
   'MediaStreamTrackEvent': _rtc_annotations,
+  'MediaSource': [
+    # TODO(alanknight): This works on Firefox 33 behind a flag and in Safari
+    # desktop, but not mobile. On theory that static false positives are worse
+    # than negatives, leave those out for now. Update once they're available.
+    "@SupportedBrowser(SupportedBrowser.CHROME)",
+    "@SupportedBrowser(SupportedBrowser.IE, '11')",
+  ],
   'MutationObserver': [
     "@SupportedBrowser(SupportedBrowser.CHROME)",
     "@SupportedBrowser(SupportedBrowser.FIREFOX)",
     "@SupportedBrowser(SupportedBrowser.SAFARI)",
     "@Experimental()",
   ],
   'NotificationCenter': _webkit_experimental_annotations,
   'Performance': _performance_annotations,
   'PopStateEvent': _history_annotations,
   'RTCIceCandidate': _rtc_annotations,
@@ skipping 302 matching lines @@
       pass
     else:
       _logger.warn('Unknown support_level - %s:%s' % (interface_id, member_id))
 
     return annotations
 
   def Flush(self):
     json_file = open(self._api_status_path, 'w+')
     json.dump(self._types, json_file, indent=2, separators=(',', ': '), sort_keys=True)
     json_file.close()