Devirtualize Document class type checking

Source/core/html/MediaDocument.h

 /*
  * Copyright (C) 2008,2009 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 25 matching lines @@
     {
         return adoptRef(new MediaDocument(frame, url));
     }
     virtual ~MediaDocument();
 
     void mediaElementSawUnsupportedTracks();
 
 private:
     MediaDocument(Frame*, const KURL&);
 
-    virtual bool isMediaDocument() const { return true; }        
     virtual PassRefPtr<DocumentParser> createParser();
 
     virtual void defaultEventHandler(Event*);
 
     void replaceMediaElementTimerFired(Timer<MediaDocument>*);
 
     Timer<MediaDocument> m_replaceMediaElementTimer;
 };
 
 inline MediaDocument* toMediaDocument(Document* document)
 {
     ASSERT_WITH_SECURITY_IMPLICATION(!document || document->isMediaDocument());
     return static_cast<MediaDocument*>(document);
 }
 
 inline const MediaDocument* toMediaDocument(const Document* document)
 {
     ASSERT_WITH_SECURITY_IMPLICATION(!document || document->isMediaDocument());
     return static_cast<const MediaDocument*>(document);
 }
 
 // This will catch anyone doing an unnecessary cast.
 void toMediaDocument(const MediaDocument*);
 
 }
 
 #endif