Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/modules/notifications/NotificationCenter.h

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  * Copyright (C) 2011, 2012 Apple 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.
@@ skipping 45 matching lines @@
 // FIXME: oilpan: Change this to GarbageCollectedFinalized once we move ActiveDOMObject to oilpan.
 class NotificationCenter FINAL : public RefCountedWillBeGarbageCollectedFinalized<NotificationCenter>, public ScriptWrappable, public ActiveDOMObject {
     DECLARE_GC_INFO;
 public:
     static PassRefPtrWillBeRawPtr<NotificationCenter> create(ExecutionContext*, NotificationClient*);
 
     PassRefPtrWillBeRawPtr<WebKitNotification> createNotification(const String& iconUrl, const String& title, const String& body, ExceptionState& exceptionState)
     {
         if (!client()) {
             exceptionState.throwDOMException(InvalidStateError, "The notification client is null.");
-            return 0;
+            return nullptr;
         }
         return WebKitNotification::create(title, body, iconUrl, executionContext(), exceptionState, this);
     }
 
     NotificationClient* client() const { return m_client; }
 
     int checkPermission();
     void requestPermission(PassOwnPtr<VoidCallback> = nullptr);
 
     virtual void stop() OVERRIDE;
@@ skipping 29 matching lines @@
 // FIXME: oilpan: Move this to ThreadState.h.
 template<> struct ThreadingTrait<NotificationCenter::NotificationRequestCallback> {
     static const ThreadAffinity Affinity = AnyThread;
 };
 
 } // namespace WebCore
 
 #endif // ENABLE(LEGACY_NOTIFICATIONS)
 
 #endif // NotificationCenter_h