Merge "[User Switcher] Add user and guest on bg thread." into tm-qpr-dev am: 57f5c6bc

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/19324250



Change-Id: I190aa99f5cb86d63ea47878549f97754672b8a8c
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>