Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/animation/AnimatableNeutral.h

 /*
  * Copyright (C) 2013 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 26 matching lines @@
 
 class AnimatableNeutral FINAL : public AnimatableValue {
 public:
     virtual ~AnimatableNeutral() { }
 
 protected:
     static PassRefPtr<AnimatableNeutral> create() { return adoptRef(new AnimatableNeutral()); }
     virtual PassRefPtr<AnimatableValue> interpolateTo(const AnimatableValue* value, double fraction) const OVERRIDE
     {
         ASSERT_NOT_REACHED();
-        return 0;
+        return nullptr;
     }
 
 private:
     friend class AnimatableValue;
     virtual AnimatableType type() const OVERRIDE { return TypeNeutral; }
     virtual bool equalTo(const AnimatableValue* value) const OVERRIDE
     {
         ASSERT_NOT_REACHED();
         return true;
     }
 };
 
 } // namespace WebCore
 
 #endif // AnimatableNeutral_h