Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/plugins/DOMMimeType.cpp

 /*
  *  Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
  *
  *  This library is free software; you can redistribute it and/or
  *  modify it under the terms of the GNU Lesser General Public
  *  License as published by the Free Software Foundation; either
  *  version 2 of the License, or (at your option) any later version.
  *
  *  This library is distributed in the hope that it will be useful,
  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 52 matching lines @@
 {
     return mimeClassInfo().desc;
 }
 
 PassRefPtrWillBeRawPtr<DOMPlugin> DOMMimeType::enabledPlugin() const
 {
     // FIXME: allowPlugins is just a client call. We should not need
     // to bounce through the page or mainframe or loader to get there.
     // Something like: m_frame->host()->client()->allowPlugins().
     if (!m_frame || !m_frame->page() || !m_frame->page()->mainFrame()->loader().allowPlugins(NotAboutToInstantiatePlugin))
-        return 0;
+        return nullptr;
 
     return DOMPlugin::create(m_pluginData.get(), m_frame, m_pluginData->mimePluginIndices()[m_index]);
 }
 
 } // namespace WebCore