Drop [TypeChecking=Nullable]; deduce from attribute type instead

Source/core/animation/AnimationNode.h

Index: Source/core/animation/AnimationNode.h
diff --git a/Source/core/animation/AnimationNode.h b/Source/core/animation/AnimationNode.h
index 4c548541b759ed75a6018c1bb9eeaf4d282f4eee..207fe10b31fc82cc81462eb11e061eab87201882 100644
--- a/Source/core/animation/AnimationNode.h
+++ b/Source/core/animation/AnimationNode.h
@@ -102,7 +102,6 @@ public:
 
     const AnimationPlayer* player() const { return m_player; }
     AnimationPlayer* player() { return m_player; }
-    AnimationPlayer* player(bool& isNull) { isNull = !m_player; return m_player; }
     const Timing& specifiedTiming() const { return m_timing; }
     PassRefPtrWillBeRawPtr<AnimationNodeTiming> timing();
     void updateSpecifiedTiming(const Timing&);