Merge "Add an observer class for transition lifecycles" into tm-qpr-dev am:...

Merge "Add an observer class for transition lifecycles" into tm-qpr-dev am: cbb61207 am: e9bd95ca

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/19582591



Change-Id: I6bb4bde44f299025f6a7d13b450408312cda73aa
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>