Prevent ExtendableMessageEvent.data from thwarting DOM tree-shaking

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 140 matching lines @@
       "@Creates('Null')",
       "@Returns('EventTarget|=Object')",
     ],
 
     # Only nodes in the DOM bubble and have target !== currentTarget.
     'Event.target': [
       "@Creates('Node')",
       "@Returns('EventTarget|=Object')",
     ],
 
+    # TODO(sra): Investigate how ExtendableMessageEvent.data is different from
+    # MessageEvent.data. It might be necessary to put in a method to translate
+    # the JavaScript wire type into a Dart type.

[Jacob, 2017/05/12 02:41:36]

Yeah this is most likely busted as is. 

+    'ExtendableMessageEvent.data': [
+      "@annotation_Creates_SerializedScriptValue",
+      "@annotation_Returns_SerializedScriptValue",
+    ],
+
+    # TODO(sra): We could determine the following by parsing the compound IDL
+    # type.
+    'ExtendableMessageEvent.source': [
+      "@Creates('Client|_ServiceWorker|MessagePort')",
+      "@Returns('Client|_ServiceWorker|MessagePort|Null')",
+    ],
+
     'File.lastModifiedDate': [
       "@Creates('Null')", # JS date object.
     ],
 
     'FocusEvent.relatedTarget': [
       "@Creates('Null')",
     ],
 
     'Gamepad.buttons': [
         "@Creates('JSExtendableArray|GamepadButton')",
@@ skipping 735 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()