Merge "Add a callback to listen to uid foreground-ness change." into udc-dev am: b0302b10 am: 31fb0397

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



Change-Id: I0d528ac70315715e3879bda44dff70d5adbee9f6
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>