Merge "Setting/getting per-screen wallpaper (2/3)." into tm-qpr-dev am: 8ca34bc0d4 am: 2a18f36665

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/ThemePicker/+/20920224

Change-Id: I18200f5126b9f9bf3b3d79eec1a8c60d25fd6a7f
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>