Merge "Add an extra transition type in TransitSession for custom transition." into udc-dev am: e4c4d532 am: ec251781

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



Change-Id: I42f1f41285d00783e145a87b60a967aeba7362d6
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>