Introduce DEFINE_ANIMATABLE_VALUE_TYPE_CASTS to replace manual toFoo() for animatable value

Source/core/animation/AnimatableImage.h

Index: Source/core/animation/AnimatableImage.h
diff --git a/Source/core/animation/AnimatableImage.h b/Source/core/animation/AnimatableImage.h
index ae048d227180ae0929ac018abd00ad38c201cfb5..40152f95c5e6d42455e8b1bc9373d4639486872c 100644
--- a/Source/core/animation/AnimatableImage.h
+++ b/Source/core/animation/AnimatableImage.h
@@ -63,11 +63,7 @@ private:
     const RefPtr<StyleImage> m_image;
 };
 
-inline const AnimatableImage* toAnimatableImage(const AnimatableValue* value)
-{
-    ASSERT_WITH_SECURITY_IMPLICATION(value && value->isImage());
-    return static_cast<const AnimatableImage*>(value);
-}
+DEFINE_ANIMATABLE_VALUE_TYPE_CASTS(AnimatableImage, isImage());
 
 } // namespace WebCore