Refactoring: Add toWebFrameImpl() interface.

Source/web/WebFrameImpl.h

 /*
  * Copyright (C) 2009 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 481 matching lines @@
     OwnPtr<ChromePrintContext> m_printContext;
 
     // The identifier of this frame.
     long long m_identifier;
 
     // Ensure we don't overwrite valid history data during same document loads
     // from HistoryItems
     bool m_inSameDocumentHistoryLoad;
 };
 
+inline WebFrameImpl* toWebFrameImpl(WebFrame* webFrame)
+{
+    return static_cast<WebFrameImpl*>(webFrame);
+}
+
+inline const WebFrameImpl* toWebFrameImpl(const WebFrame* webFrame)
+{
+    return static_cast<const WebFrameImpl*>(webFrame);
+}
+
+// This will catch anyone doing an unnecessary cast.
+void toWebFrameImpl(const WebFrameImpl*);
+
 } // namespace WebKit
 
 #endif