Start changing WebDOMMessageEvent for using target execution context.

Source/web/WebDOMMessageEvent.cpp

Index: Source/web/WebDOMMessageEvent.cpp
diff --git a/Source/web/WebDOMMessageEvent.cpp b/Source/web/WebDOMMessageEvent.cpp
index 573ae5495198011867ed41ef341f4c9b3239de4f..61a70a1e46833bc28dc7f2b02d10cbc7b5c96406 100644
--- a/Source/web/WebDOMMessageEvent.cpp
+++ b/Source/web/WebDOMMessageEvent.cpp
@@ -37,12 +37,30 @@
 #include "core/events/MessageEvent.h"
 #include "core/frame/LocalDOMWindow.h"
 #include "public/platform/WebString.h"
+#include "public/web/WebDocument.h"
 #include "public/web/WebFrame.h"
 #include "public/web/WebSerializedScriptValue.h"
 #include "web/WebLocalFrameImpl.h"
 
 namespace blink {
 
+void WebDOMMessageEvent::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& webChannels)
+{
+    ASSERT(m_private.get());
+    ASSERT(isMessageEvent());
+    DOMWindow* window = nullptr;
+    // TODO(alexmos): Figure out if this is the right thing to do.

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

Would hate to leave this TODO in the new version. Perhaps we can get it fixed
right now?

[alexmos, 2015/08/15 01:07:02]

I think we can just remove this.  dcheng@ originally added it in
https://codereview.chromium.org/683013002.  Unless Daniel meant something else,
I don't see a reason for keeping it, as this already works correctly for both
local and remote cases.

[sgurun-gerrit only, 2015/08/15 01:12:11]

Done.

+    if (sourceFrame)
+        window = toCoreFrame(sourceFrame)->domWindow();
+    RefPtrWillBeRawPtr<Document> coreDocument = PassRefPtrWillBeRawPtr<Document>(targetDocument);
+    MessagePortArray* ports = MessagePort::toMessagePortArray(coreDocument.get(), webChannels);
+    // Use an empty array for |ports| when it is null because this function
+    // is used to implement postMessage().
+    if (!ports)
+        ports = new MessagePortArray;
+    unwrap<MessageEvent>()->initMessageEvent(type, canBubble, cancelable, messageData, origin, lastEventId, window, ports);
+}
+
 void WebDOMMessageEvent::initMessageEvent(const WebString& type, bool canBubble, bool cancelable, const WebSerializedScriptValue& messageData, const WebString& origin, const WebFrame* sourceFrame, const WebString& lastEventId, const WebMessagePortChannelArray& webChannels)
 {
     ASSERT(m_private.get());