Merge "[User Switcher] Make add button pillshaped." into tm-qpr-dev am: 1610b74ecc

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/20315107

Change-Id: Ic230f81a67a9e5d4a1be450fa7f931609c5d5662
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>