Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/html/HTMLLinkElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2003, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Rob Buis (rwlbuis@gmail.com)
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 440 matching lines @@
 {
     ASSERT(m_pendingSheetType < Blocking);
     addPendingSheet(Blocking);
 }
 
 void LinkStyle::clearSheet()
 {
     ASSERT(m_sheet);
     ASSERT(m_sheet->ownerNode() == m_owner);
     m_sheet->clearOwnerNode();
-    m_sheet = 0;
+    m_sheet = nullptr;
 }
 
 bool LinkStyle::styleSheetIsLoading() const
 {
     if (m_loading)
         return true;
     if (!m_sheet)
         return false;
     return m_sheet->contents()->isLoading();
 }
@@ skipping 154 matching lines @@
 void LinkStyle::ownerRemoved()
 {
     if (m_sheet)
         clearSheet();
 
     if (styleSheetIsLoading())
         removePendingSheet(RemovePendingSheetNotifyLater);
 }
 
 } // namespace WebCore