Merge "Implement encoding alpha8 gainmaps" into udc-dev am: 492ddfb5

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/21656499



Change-Id: I0656ab9a7914fca1848c036c42693a769057fb33
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>