Add more missing closing namespace comments.

third_party/WebKit/Source/core/dom/UserActionElementSet.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.
  *     * Neither the name of Google Inc. nor the names of its
@@ skipping 106 matching lines @@
     m_elements.add(element, flags);
 }
 
 DEFINE_TRACE(UserActionElementSet)
 {
 #if ENABLE(OILPAN)
     visitor->trace(m_elements);
 #endif
 }
 
-}
+} // namespace blink