Introduce DEFINE_DOCUMENT_TYPE_CASTS, and use it

Source/core/html/ImageDocument.h

 /*
  * Copyright (C) 2006, 2007, 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 54 matching lines @@
     // Whether enough of the image has been loaded to determine its size
     bool m_imageSizeIsKnown;
 
     // Whether the image is shrunk to fit or not
     bool m_didShrinkImage;
 
     // Whether the image should be shrunk or not
     bool m_shouldShrinkImage;
 };
 
-inline ImageDocument* toImageDocument(Document* document)
-{
-    ASSERT_WITH_SECURITY_IMPLICATION(!document || document->isImageDocument());
-    return static_cast<ImageDocument*>(document);
-}
-
-inline const ImageDocument* toImageDocument(const Document* document)
-{
-    ASSERT_WITH_SECURITY_IMPLICATION(!document || document->isImageDocument());
-    return static_cast<const ImageDocument*>(document);
-}
-
-// This will catch anyone doing an unnecessary cast.
-void toImageDocument(const ImageDocument*);
+DEFINE_DOCUMENT_TYPE_CASTS(ImageDocument);
 
 }
 
 #endif // ImageDocument_h