DO NOT MERGE Disallow Wallpaper service to launch activity from background. am: 4c065abfaf

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/24077613

Change-Id: I460329ec723574d0985b342a3021ed7291832e39
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>