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

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

Change-Id: I40c498de59fe4372963711c4417dff6878c02a0e
Signed-off-by: Automerger Merge Worker <[email protected]>