Reduce forward declarations in core/dom

Source/core/dom/custom/CustomElementRegistrationContext.h

 /*
  * Copyright (C) 2013 Google 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
@@ skipping 26 matching lines @@
 #include "core/dom/custom/CustomElementUpgradeCandidateMap.h"
 #include "platform/heap/Handle.h"
 #include "wtf/HashMap.h"
 #include "wtf/PassOwnPtr.h"
 #include "wtf/PassRefPtr.h"
 #include "wtf/text/AtomicString.h"
 
 namespace WebCore {
 
 class CustomElementConstructorBuilder;
-class CustomElementDefinition;
 class Document;
 class Element;
 class ExceptionState;
 
 class CustomElementRegistrationContext FINAL : public RefCountedWillBeGarbageCollectedFinalized<CustomElementRegistrationContext> {
 public:
     static PassRefPtrWillBeRawPtr<CustomElementRegistrationContext> create()
     {
         return adoptRefWillBeNoop(new CustomElementRegistrationContext());
     }
@@ skipping 23 matching lines @@
     CustomElementRegistry m_registry;
 
     // Element creation
     OwnPtrWillBeMember<CustomElementUpgradeCandidateMap> m_candidates;
 };
 
 }
 
 #endif // CustomElementRegistrationContext_h