Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/html/HTMLPlugInElement.cpp

 /**
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Stefan Schimanski (1Stein@gmx.de)
  * Copyright (C) 2004, 2005, 2006 Apple Computer, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 140 matching lines @@
         setNeedsWidgetUpdate(true);
     if (m_isDelayingLoadEvent) {
         m_isDelayingLoadEvent = false;
         document().decrementLoadEventDelayCount();
     }
 
     resetInstance();
 
     if (m_isCapturingMouseEvents) {
         if (Frame* frame = document().frame())
-            frame->eventHandler().setCapturingMouseEventsNode(0);
+            frame->eventHandler().setCapturingMouseEventsNode(nullptr);
         m_isCapturingMouseEvents = false;
     }
 
     if (m_NPObject) {
         _NPN_ReleaseObject(m_NPObject);
         m_NPObject = 0;
     }
 
     HTMLFrameOwnerElement::detach(context);
 }
@@ skipping 359 matching lines @@
     if (root.isOldestAuthorShadowRoot())
         lazyReattachIfAttached();
 }
 
 bool HTMLPlugInElement::useFallbackContent() const
 {
     return hasAuthorShadowRoot();
 }
 
 }