Reduce forward declarations in core/dom

Source/core/dom/ElementDataCache.h

 /*
  * Copyright (C) 2012, 2013 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 20 matching lines @@
 #include "wtf/PassOwnPtr.h"
 #include "wtf/PassRefPtr.h"
 #include "wtf/RefPtr.h"
 #include "wtf/Vector.h"
 #include "wtf/text/StringHash.h"
 
 namespace WebCore {
 
 class Attribute;
 class ShareableElementData;
-class ShareableElementDataCacheEntry;
 
 class ElementDataCache {
 public:
     static PassOwnPtr<ElementDataCache> create() { return adoptPtr(new ElementDataCache); }
     ~ElementDataCache();
 
     PassRefPtr<ShareableElementData> cachedShareableElementDataWithAttributes(const Vector<Attribute>&);
 
 private:
     ElementDataCache();
 
     typedef HashMap<unsigned, RefPtr<ShareableElementData>, AlreadyHashed> ShareableElementDataCache;
     ShareableElementDataCache m_shareableElementDataCache;
 };
 
 }
 
 #endif