Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/platform/Length.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, 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Andrew Wellington (proton@wiretapped.net)
  *
  * 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
@@ skipping 131 matching lines @@
         ASSERT(m_map.contains(index));
         return m_map.get(index);
     }
 
     void decrementRef(int index)
     {
         ASSERT(m_map.contains(index));
         CalculationValue* value = m_map.get(index);
         if (value->hasOneRef()) {
             // Force the CalculationValue destructor early to avoid a potential recursive call inside HashMap remove().
-            m_map.set(index, 0);
+            m_map.set(index, nullptr);
             m_map.remove(index);
         } else {
             value->deref();
         }
     }
 
 private:
     int m_index;
     HashMap<int, RefPtr<CalculationValue> > m_map;
 };
@@ skipping 49 matching lines @@
     return isCalculated() && (calculationValue() == o.calculationValue() || *calculationValue() == *o.calculationValue());
 }
 
 struct SameSizeAsLength {
     int32_t value;
     int32_t metaData;
 };
 COMPILE_ASSERT(sizeof(Length) == sizeof(SameSizeAsLength), length_should_stay_small);
 
 } // namespace WebCore