Remove forward declarations from Source/core/dom/custom

Source/core/dom/custom/CustomElement.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 25 matching lines @@
 #include "wtf/Noncopyable.h"
 #include "wtf/PassRefPtr.h"
 #include "wtf/RefPtr.h"
 #include "wtf/Vector.h"
 #include "wtf/text/AtomicString.h"
 
 namespace blink {
 
 class CustomElementMicrotaskImportStep;
 class Document;
-class Element;
 class HTMLImportChild;
 
 class CustomElement {
 public:
     enum NameSet {
         EmbedderNames = 1 << 0,
         StandardNames = 1 << 1,
         AllNames = EmbedderNames | StandardNames
     };
     static bool isValidName(const AtomicString& name, NameSet validNames = AllNames);
@@ skipping 12 matching lines @@
     static void didAttach(Element*, const Document&);
     static void didDetach(Element*, const Document&);
     static void wasDestroyed(Element*);
 
 private:
     CustomElement();
 
     static Vector<AtomicString>& embedderCustomElementNames();
 };
 
-}
+} // namespace blink
 
 #endif // CustomElement_h