Refactoring: Add toWebFrameImpl() interface.

Source/web/ChromeClientImpl.cpp

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).
  *
  * 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.
@@ skipping 332 matching lines @@
 }
 
 bool ChromeClientImpl::statusbarVisible()
 {
     return m_statusbarVisible;
 }
 
 void ChromeClientImpl::setScrollbarsVisible(bool value)
 {
     m_scrollbarsVisible = value;
-    WebFrameImpl* webFrame = static_cast<WebFrameImpl*>(m_webView->mainFrame());
+    WebFrameImpl* webFrame = toWebFrameImpl(m_webView->mainFrame());
     if (webFrame)
         webFrame->setCanHaveScrollbars(value);
 }
 
 bool ChromeClientImpl::scrollbarsVisible()
 {
     return m_scrollbarsVisible;
 }
 
 void ChromeClientImpl::setMenubarVisible(bool value)
@@ skipping 652 matching lines @@
 {
 }
 
 void NavigatorContentUtilsClientImpl::registerProtocolHandler(const String& scheme, const String& baseURL, const String& url, const String& title)
 {
     m_webView->client()->registerProtocolHandler(scheme, baseURL, url, title);
 }
 #endif
 
 } // namespace WebKit