Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/css/CSSImageGeneratorValue.cpp

 /*
  * Copyright (C) 2008 Apple 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 104 matching lines @@
         return toCSSCanvasValue(this)->image(renderer, size);
     case CrossfadeClass:
         return toCSSCrossfadeValue(this)->image(renderer, size);
     case LinearGradientClass:
         return toCSSLinearGradientValue(this)->image(renderer, size);
     case RadialGradientClass:
         return toCSSRadialGradientValue(this)->image(renderer, size);
     default:
         ASSERT_NOT_REACHED();
     }
-    return 0;
+    return nullptr;
 }
 
 bool CSSImageGeneratorValue::isFixedSize() const
 {
     switch (classType()) {
     case CanvasClass:
         return toCSSCanvasValue(this)->isFixedSize();
     case CrossfadeClass:
         return toCSSCrossfadeValue(this)->isFixedSize();
     case LinearGradientClass:
@@ skipping 71 matching lines @@
         break;
     case RadialGradientClass:
         toCSSRadialGradientValue(this)->loadSubimages(fetcher);
         break;
     default:
         ASSERT_NOT_REACHED();
     }
 }
 
 } // namespace WebCore