Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/animation/CompositorAnimationsTest.cpp

Index: Source/core/animation/CompositorAnimationsTest.cpp
diff --git a/Source/core/animation/CompositorAnimationsTest.cpp b/Source/core/animation/CompositorAnimationsTest.cpp
index e06fdf99469f6bf11b50a6ce1b39eef89f0fdbac..ed54999eb48a505884b6692240cf400739fa5c6f 100644
--- a/Source/core/animation/CompositorAnimationsTest.cpp
+++ b/Source/core/animation/CompositorAnimationsTest.cpp
@@ -182,7 +182,7 @@ public:
         return frames;
     }
 
-    PassRefPtr<KeyframeEffectModel> createKeyframeEffectModel(PassRefPtr<Keyframe> prpFrom, PassRefPtr<Keyframe> prpTo, PassRefPtr<Keyframe> prpC = 0, PassRefPtr<Keyframe> prpD = 0)
+    PassRefPtr<KeyframeEffectModel> createKeyframeEffectModel(PassRefPtr<Keyframe> prpFrom, PassRefPtr<Keyframe> prpTo, PassRefPtr<Keyframe> prpC = nullptr, PassRefPtr<Keyframe> prpD = nullptr)
     {
         RefPtr<Keyframe> from = prpFrom;
         RefPtr<Keyframe> to = prpTo;