Devirtualize Document class type checking

Source/core/html/PluginDocument.h

 /*
  * Copyright (C) 2006, 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 36 matching lines @@
     virtual void detach() OVERRIDE;
 
     void cancelManualPluginLoad();
 
     bool shouldLoadPluginManually() { return m_shouldLoadPluginManually; }
 
 private:
     PluginDocument(Frame*, const KURL&);
 
     virtual PassRefPtr<DocumentParser> createParser() OVERRIDE;
-    virtual bool isPluginDocument() const OVERRIDE { return true; }    
         
     void setShouldLoadPluginManually(bool loadManually) { m_shouldLoadPluginManually = loadManually; }
 
     bool m_shouldLoadPluginManually;
     RefPtr<Node> m_pluginNode;
 };
 
 inline PluginDocument* toPluginDocument(Document* document)
 {
     ASSERT_WITH_SECURITY_IMPLICATION(!document || document->isPluginDocument());
     return static_cast<PluginDocument*>(document);
 }
 
 inline const PluginDocument* toPluginDocument(const Document* document)
 {
     ASSERT_WITH_SECURITY_IMPLICATION(!document || document->isPluginDocument());
     return static_cast<const PluginDocument*>(document);
 }
 
 // This will catch anyone doing an unnecessary cast.
 void toPluginDocument(const PluginDocument*);
     
 }
 
 #endif // PluginDocument_h