Merge "Check DreamActivity callback type to prevent class cast exception" into tm-qpr-dev am: 8daaa631f2

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/21938299

Change-Id: I3b9faf4a4a96fe1b406784b71d6f278bf4bdf692
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>