Remove forward declarations from Source/core/dom/custom

Source/core/dom/custom/CustomElementDefinition.cpp

 /*
  * Copyright (C) 2012 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 26 matching lines @@
 {
     return adoptRef(new CustomElementDefinition(descriptor, callbacks));
 }
 
 CustomElementDefinition::CustomElementDefinition(const CustomElementDescriptor& descriptor, PassRefPtr<CustomElementLifecycleCallbacks> callbacks)
     : m_descriptor(descriptor)
     , m_callbacks(callbacks)
 {
 }
 
-}
+} // namespace blink