[automerger skipped] Add the thread-safe protection for PowerAllowlistBackend if possible am: da0da5ab92 -s ours

am skip reason: Merged-In I3b9e76889db7807496e38371d735ca41160be88e with SHA-1 2bf606972e is already in history

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/27341935

Change-Id: Iad3fe03699e54f2f9930b51db1c006b1e2bca062
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>