Merge "Add a callback to listen to uid foreground-ness change." into udc-dev...

Merge "Add a callback to listen to uid foreground-ness change." into udc-dev am: b0302b10 am: cff2001b

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/22499498



Change-Id: If35152b7075e989cfb7652c4ffb8d8d882f73d6b
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>