Merge "BackEvent: add generated events for fling gesture" into udc-dev am: 89f8d9ca am: 8f50fc63

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/21510847



Change-Id: I0634393894903f4ffc6175f268ecb26d1294a5fc
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>