DO NOT MERGE Disallow Wallpaper service to launch activity from background. am: 8efec2c095 am: 1b7d87139c

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/23912846

Change-Id: Ide2654a3580d4c10ae92af1e1c1562b1fae8105a
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>