Merge "Allow WindowState to assign layer during transition." into udc-dev am: 28017afd am: 4d6ffc33 am: 30df0345 am: 1cbdae0b

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/23127077



Change-Id: I68e6847e5f2c2056cfedbf9db2bfa73989cf078d
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>