Merge "Allow WindowState to assign layer during transition." into udc-dev am: 28017afd52 am: bcfbc01de8 am: 1a81c0d0e7

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

Change-Id: I852c6c892f805e12b3176f017b9d375d0f7cd782
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>