Store IdTargetObserver::m_registry as a reference

Source/core/dom/IdTargetObserver.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:
  * 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 13 matching lines @@
  */
 
 #include "config.h"
 #include "core/dom/IdTargetObserver.h"
 
 #include "core/dom/IdTargetObserverRegistry.h"
 
 namespace WebCore {
 
 IdTargetObserver::IdTargetObserver(IdTargetObserverRegistry& registry, const AtomicString& id)
-    : m_registry(&registry)
+    : m_registry(registry)
     , m_id(id)
 {
-    m_registry->addObserver(m_id, this);
+    m_registry.addObserver(m_id, this);
 }
 
 IdTargetObserver::~IdTargetObserver()
 {
-    if (m_registry)
-        m_registry->removeObserver(m_id, this);
+    m_registry.removeObserver(m_id, this);
 }
 
 } // namespace WebCore