Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/css/PropertySetCSSStyleDeclaration.cpp

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2011 Research In Motion Limited. 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
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 151 matching lines @@
 
     didMutate(PropertyChanged);
 
     mutationScope.enqueueMutationRecord();
 }
 
 PassRefPtrWillBeRawPtr<CSSValue> AbstractPropertySetCSSStyleDeclaration::getPropertyCSSValue(const String& propertyName)
 {
     CSSPropertyID propertyID = cssPropertyID(propertyName);
     if (!propertyID)
-        return 0;
+        return nullptr;
     return cloneAndCacheForCSSOM(propertySet()->getPropertyCSSValue(propertyID).get());
 }
 
 String AbstractPropertySetCSSStyleDeclaration::getPropertyValue(const String &propertyName)
 {
     CSSPropertyID propertyID = cssPropertyID(propertyName);
     if (!propertyID)
         return String();
     return propertySet()->getPropertyValue(propertyID);
 }
@@ skipping 205 matching lines @@
 {
     m_parentElement->ref();
 }
 
 void InlineCSSStyleDeclaration::deref()
 {
     m_parentElement->deref();
 }
 
 } // namespace WebCore