Add more missing closing namespace comments.

third_party/WebKit/Source/core/page/PopupOpeningObserver.h

 /*
  * 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:
  * 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 @@
 namespace blink {
 
 class CORE_EXPORT PopupOpeningObserver {
 public:
     virtual void willOpenPopup() = 0;
 
 protected:
     virtual ~PopupOpeningObserver() { }
 };
 
-}
+} // namespace blink
 #endif