Add more missing closing namespace comments.

third_party/WebKit/Source/platform/heap/CallbackStack.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "platform/heap/CallbackStack.h"
 
 namespace blink {
 
 void CallbackStack::Block::clear()
 {
@@ skipping 123 matching lines @@
 bool CallbackStack::hasCallbackForObject(const void* object)
 {
     for (Block* current = m_first; current; current = current->next()) {
         if (current->hasCallbackForObject(object))
             return true;
     }
     return false;
 }
 #endif
 
-}
+} // namespace blink