Avoid copy in LayoutAnimationDriver

Summary:
changelog: [internal]

Avoid unnecessary copy of `ShadowViewMutation` and `ShadowView`.

Reviewed By: RSNara

Differential Revision: D30756214

fbshipit-source-id: 39c44dd60582e6c111986df482613212e25739d7

ReactCommon/react/renderer/animations/LayoutAnimationDriver.cpp

@@ -55,19 +55,12 @@ void LayoutAnimationDriver::animationMutationsForFrame(
           animationInterpolationFactor, baselineShadowView, finalShadowView);
 
       // Create the mutation instruction
-      auto updateMutation = ShadowViewMutation::UpdateMutation(
-          keyframe.viewPrev, mutatedShadowView);
+      mutationsList.emplace_back(ShadowViewMutation::UpdateMutation(
+          keyframe.viewPrev, mutatedShadowView));
 
-      // All generated Update mutations must have an "old" and "new"
-      // ShadowView. Checking for nonzero tag doesn't guarantee that the views
-      // are valid/correct, just that something is there.
-      react_native_assert(updateMutation.oldChildShadowView.tag > 0);
-      react_native_assert(updateMutation.newChildShadowView.tag > 0);
-
-      mutationsList.push_back(updateMutation);
       PrintMutationInstruction("Animation Progress:", updateMutation);
 
-      keyframe.viewPrev = mutatedShadowView;
+      keyframe.viewPrev = std::move(mutatedShadowView);
 
       if (animationTimeProgressLinear < 1) {
         incompleteAnimations++;