Merge "Polish activity transition for letterbox" into tm-qpr-dev am: c3a33cde

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/18320843



Change-Id: I92dc418580d4503ee80ae9d94520d4b5d2c92009
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>