Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/css/StylePropertySet.cpp

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012, 2013 Apple Inc. All rights reserved.
  * Copyright (C) 2011 Research In Motion Limited. All rights reserved.
  * Copyright (C) 2013 Intel Corporation. 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 117 matching lines @@
     if (value)
         return value->cssText();
 
     return StylePropertySerializer(*this).getPropertyValue(propertyID);
 }
 
 PassRefPtrWillBeRawPtr<CSSValue> StylePropertySet::getPropertyCSSValue(CSSPropertyID propertyID) const
 {
     int foundPropertyIndex = findPropertyIndex(propertyID);
     if (foundPropertyIndex == -1)
-        return 0;
+        return nullptr;
     return propertyAt(foundPropertyIndex).value();
 }
 
 bool MutableStylePropertySet::removeShorthandProperty(CSSPropertyID propertyID)
 {
     StylePropertyShorthand shorthand = shorthandForProperty(propertyID);
     if (!shorthand.length())
         return false;
 
     bool ret = removePropertiesInSet(shorthand.properties(), shorthand.length());
@@ skipping 420 matching lines @@
     result.appendLiteral(": ");
     result.append(propertyValue()->cssText());
     if (isImportant())
         result.appendLiteral(" !important");
     result.append(';');
     return result.toString();
 }
 
 
 } // namespace WebCore