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..b6a683ec513ac8d645fbbcf6640b7f7ba5c556bb 100644
--- a/Source/web/WebDOMMessageEvent.cpp
+++ b/Source/web/WebDOMMessageEvent.cpp
@@ -37,12 +37,29 @@
 #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;
+    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());

[dcheng, 2015/08/15 05:12:30]

Can we re-express this in terms of the new interface? Then it'll be clear
there's no difference between the old/new overloads.

[sgurun-gerrit only, 2015/08/18 15:17:30]

Done.