Merge "Prevent callback registration when back flag is disabled" into tm-dev...

Merge "Prevent callback registration when back flag is disabled" into tm-dev am: 1c6de844 am: 0592820f am: 9e2a134d

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/18794217



Change-Id: Id3181b7f8155aa5e3bda8c1604fd70a0cd290601
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>