Merge "Support for OnBackAnimationCallback: added for 3-button navigation /...

Merge "Support for OnBackAnimationCallback: added for 3-button navigation / hardware keys" into udc-dev am: b98116ac am: 54ec9577 am: 341ca50b

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/22965557



Change-Id: Ib0371aeb753a4831a8128f5eb96554132db1ff6d
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>