[DO NOT MERGE] Check caller's uid in backupAgentCreated callback am: ebdcc72a23

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/24323875

Change-Id: Idff77787bb197faaaa03fd0e2a17e7feead67d3a
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>