Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/css/BasicShapeFunctions.cpp

 /*
  * Copyright (C) 2012 Adobe Systems Incorporated. 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.
@@ skipping 57 matching lines @@
     switch (radius.type()) {
     case BasicShapeRadius::Value:
         return pool.createValue(radius.value(), style);
     case BasicShapeRadius::ClosestSide:
         return pool.createIdentifierValue(CSSValueClosestSide);
     case BasicShapeRadius::FarthestSide:
         return pool.createIdentifierValue(CSSValueFarthestSide);
     }
 
     ASSERT_NOT_REACHED();
-    return 0;
+    return nullptr;
 }
 
 PassRefPtrWillBeRawPtr<CSSValue> valueForBasicShape(const RenderStyle& style, const BasicShape* basicShape)
 {
     CSSValuePool& pool = cssValuePool();
 
     RefPtrWillBeRawPtr<CSSBasicShape> basicShapeValue;
     switch (basicShape->type()) {
     case BasicShape::BasicShapeRectangleType: {
         const BasicShapeRectangle* rectangle = static_cast<const BasicShapeRectangle*>(basicShape);
@@ skipping 339 matching lines @@
         p.setY(boxSize.height() - offset);
         break;
     default:
         ASSERT_NOT_REACHED();
     }
 
     return p;
 }
 
 }