Refactoring: Add toWebFrameImpl() interface.

Source/web/WebDOMMessageEvent.cpp

 /*
  * 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
@@ skipping 34 matching lines @@
 using namespace WebCore;
 
 namespace WebKit {
 
 void WebDOMMessageEvent::initMessageEvent(const WebString& type, bool canBubble, bool cancelable, const WebSerializedScriptValue& messageData, const WebString& origin, const WebFrame* sourceFrame, const WebString& lastEventId)
 {
     ASSERT(m_private.get());
     ASSERT(isMessageEvent());
     DOMWindow* window = 0;
     if (sourceFrame)
-        window = static_cast<const WebFrameImpl*>(sourceFrame)->frame()->domWindow();
+        window = toWebFrameImpl(sourceFrame)->frame()->domWindow();
     OwnPtr<MessagePortArray> ports;
     unwrap<MessageEvent>()->initMessageEvent(type, canBubble, cancelable, messageData, origin, lastEventId, window, ports.release());
 }
 
 WebSerializedScriptValue WebDOMMessageEvent::data() const
 {
     return WebSerializedScriptValue(constUnwrap<MessageEvent>()->dataAsSerializedScriptValue());
 }
 
 WebString WebDOMMessageEvent::origin() const
 {
     return WebString(constUnwrap<MessageEvent>()->origin());
 }
 
 } // namespace WebKit