Use type cast macro for AnimatableLengthPoint|3D instead of manual toFoo()

Source/core/animation/animatable/AnimatableLengthPoint.h

Index: Source/core/animation/animatable/AnimatableLengthPoint.h
diff --git a/Source/core/animation/animatable/AnimatableLengthPoint.h b/Source/core/animation/animatable/AnimatableLengthPoint.h
index 3c03de59459abf0ae1123146f1fab66f785d2f64..9ea3930db43b72fa3d97b472664ea9214b2222f4 100644
--- a/Source/core/animation/animatable/AnimatableLengthPoint.h
+++ b/Source/core/animation/animatable/AnimatableLengthPoint.h
@@ -63,11 +63,7 @@ private:
     RefPtrWillBeMember<AnimatableValue> m_y;
 };
 
-inline const AnimatableLengthPoint* toAnimatableLengthPoint(const AnimatableValue* value)
-{
-    ASSERT_WITH_SECURITY_IMPLICATION(value && value->isLengthPoint());
-    return static_cast<const AnimatableLengthPoint*>(value);
-}
+DEFINE_ANIMATABLE_VALUE_TYPE_CASTS(AnimatableLengthPoint, isLengthPoint());
 
 } // namespace WebCore