Merge "Add background executor fow WmShell" into tm-dev am: a73a4428 am: 9a84714b

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/17693175



Change-Id: I0ba9715c7ddd1744950cd539078ce48ef2ce3ab7
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>