Fixing JS size regression from Blink roll.

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 184 matching lines @@
     'IDBVersionChangeEvent.newVersion': [
       "@Creates('int|String|Null')",
       "@Returns('int|String|Null')",
     ],
 
     'IDBVersionChangeEvent.oldVersion': [
       "@Creates('int|String|Null')",
       "@Returns('int|String|Null')",
     ],
 
-    'MessageEvent.ports': ["@Creates('JSExtendableArray')"],
-
     'MessageEvent.data': [
       "@annotation_Creates_SerializedScriptValue",
       "@annotation_Returns_SerializedScriptValue",
     ],
 
+    'MessageEvent.ports': ["@Creates('JSExtendableArray')"],
+
+    'MessageEvent.source': [
+      "@Creates('Null')",
+      "@Returns('EventTarget|=Object')",
+    ],
+
     'Metadata.modificationTime': [
       "@Creates('Null')", # JS date object.
     ],
 
     'MouseEvent.relatedTarget': [
       "@Creates('Node')",
       "@Returns('EventTarget|=Object')",
     ],
 
     'PopStateEvent.state': [
@@ skipping 534 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()