Merge "Add an extra transition type in TransitSession for custom transition." into udc-dev am: e4c4d532 am: 58721111 am: 4e2eede1

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/22802760



Change-Id: I23841e7cf3124c2df802b0a008b56fe0208d15f2
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>