Remove forward declarations from Source/core/dom/custom

Source/core/dom/custom/CustomElementLifecycleCallbacks.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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 46 matching lines @@
     virtual void detached(Element*) = 0;
     virtual void attributeChanged(Element*, const AtomicString& name, const AtomicString& oldValue, const AtomicString& newValue) = 0;
 
 protected:
     CustomElementLifecycleCallbacks(CallbackType type) : m_callbackType(type) { }
 
 private:
     CallbackType m_callbackType;
 };
 
-}
+} // namespace blink
 
 #endif // CustomElementLifecycleCallbacks_h