Devirtualize Document class type checking

Source/core/html/ImageDocument.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2010 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 147 matching lines @@
 
         document()->imageUpdated();
     }
 
     document()->finishedParsing();
 }
     
 // --------
 
 ImageDocument::ImageDocument(Frame* frame, const KURL& url)
-    : HTMLDocument(frame, url)
+    : HTMLDocument(frame, url, ImageDocumentClass)
     , m_imageElement(0)
     , m_imageSizeIsKnown(false)
     , m_didShrinkImage(false)
     , m_shouldShrinkImage(shouldShrinkToFit())
 {
     setCompatibilityMode(QuirksMode);
     lockCompatibilityMode();
 }
     
 PassRefPtr<DocumentParser> ImageDocument::createParser()
@@ skipping 216 matching lines @@
 void ImageDocumentElement::didMoveToNewDocument(Document* oldDocument)
 {
     if (m_imageDocument) {
         m_imageDocument->disconnectImageElement();
         m_imageDocument = 0;
     }
     HTMLImageElement::didMoveToNewDocument(oldDocument);
 }
 
 }