[automerger skipped] DO NOT MERGE Split BackEvent into an internal BackMotionEvent and public BackEvent. am: 2c2265c345 am: 3ddae35703 -s ours

am skip reason: subject contains skip directive

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/20841116

Change-Id: Iee6a6ea265c5bfb72975200163add48adc6d5c1d
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>