Merge "Add tests for the new back affordance." into tm-qpr-dev am: ca62c52a am: acc3b8b0

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/21251382



Change-Id: I172f05b54f1fe74a9b54fb10227e412b92421cff
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>