Introduce DEFINE_ANIMATABLE_VALUE_TYPE_CASTS to replace manual toFoo() for animatable value

Source/core/animation/AnimatableValue.h

Index: Source/core/animation/AnimatableValue.h
diff --git a/Source/core/animation/AnimatableValue.h b/Source/core/animation/AnimatableValue.h
index 76ce4743517915e1bd4c895c98686346617510a1..023b1ff4a66cdb6b7ffeb8003db8ee2af7ee928f 100644
--- a/Source/core/animation/AnimatableValue.h
+++ b/Source/core/animation/AnimatableValue.h
@@ -123,6 +123,9 @@ private:
     virtual bool equalTo(const AnimatableValue*) const = 0;
 };
 
+#define DEFINE_ANIMATABLE_VALUE_TYPE_CASTS(thisType, predicate) \
+    DEFINE_TYPE_CASTS(thisType, AnimatableValue, value, value->predicate, value.predicate)
+
 } // namespace WebCore
 
 #endif // AnimatableValue_h