Start changing WebDOMMessageEvent for using target execution context.

public/web/WebDOMMessageEvent.h

-/*
+ /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
  * copyright notice, this list of conditions and the following disclaimer
@@ skipping 28 matching lines @@
 #endif
 
 namespace blink {
 
 class WebFrame;
 class WebString;
 
 class WebDOMMessageEvent : public WebDOMEvent {
 public:
     WebDOMMessageEvent() { }
+    BLINK_EXPORT void initMessageEvent(const WebString& type, bool canBubble, bool cancelable, const WebSerializedScriptValue& messageData, const WebString& origin, const WebFrame* sourceFrame, const WebDocument& targetDocument, const WebString& lastEventId, const WebMessagePortChannelArray& channels = WebMessagePortChannelArray());

[adamk, 2015/08/15 00:01:16]

You'll need someone in public/OWNERS to review this API change.

     BLINK_EXPORT void initMessageEvent(const WebString& type, bool canBubble, bool cancelable, const WebSerializedScriptValue& messageData, const WebString& origin, const WebFrame* sourceFrame, const WebString& lastEventId, const WebMessagePortChannelArray& channels = WebMessagePortChannelArray());
 
     BLINK_EXPORT WebSerializedScriptValue data() const;
     BLINK_EXPORT WebString origin() const;
 
     BLINK_EXPORT WebMessagePortChannelArray releaseChannels();
 
 #if BLINK_IMPLEMENTATION
     explicit WebDOMMessageEvent(const PassRefPtrWillBeRawPtr<MessageEvent>& e) : WebDOMEvent(e) { }
 #endif
 };
 
 } // namespace blink
 
 #endif