Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/html/parser/HTMLFormattingElementList.h

 /*
  * Copyright (C) 2010 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 36 matching lines @@
     // access to Entry::isMarker() and Entry::replaceElement() to do so.
     class Entry {
     public:
         // Inline because they're hot and Vector<T> uses them.
         explicit Entry(PassRefPtr<HTMLStackItem> item)
             : m_item(item)
         {
         }
         enum MarkerEntryType { MarkerEntry };
         explicit Entry(MarkerEntryType)
-            : m_item(0)
+            : m_item(nullptr)
         {
         }
         ~Entry() {}
 
         bool isMarker() const { return !m_item; }
 
         PassRefPtr<HTMLStackItem> stackItem() const { return m_item; }
         Element* element() const
         {
             // The fact that !m_item == isMarker() is an implementation detail
@@ skipping 64 matching lines @@
     // These functions enforce the "Noah's Ark" condition, which removes redundant mis-nested elements.
     void tryToEnsureNoahsArkConditionQuickly(HTMLStackItem*, Vector<HTMLStackItem*>& remainingCandiates);
     void ensureNoahsArkCondition(HTMLStackItem*);
 
     Vector<Entry> m_entries;
 };
 
 }
 
 #endif // HTMLFormattingElementList_h