Merge "Notify when quickstep gesture starts" into sc-dev am: 44273420 am: 99fdf3b8 am: 37d4d732

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/14629807

Change-Id: Ie83f63c24f3eba3fdde473149d38a5203699d02b