Merge "Removing back-button alpha controlling logic" into tm-qpr-dev am: 1c02d77c

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/19915767



Change-Id: I38b72f7f76c071437488439f627e3142967ff19b
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>