Fix child caching in opacity_layer (#17914)

Choose a child more likely to remain stable from frame to frame as the target to cache in the OpacityLayer.
https://dart.googlesource.com/external/github.com/flutter/engine/+/efe3f4569a6aa49935ffb9a688812f46a2971b89
1 file changed
tree: 8541e7d393550ff74a3c4754a878bbe42d36bf01
  1. commits.json