Merge "Null checking window before starting dream" into tm-qpr-dev am: 3ca388e8 am: 4ab949d7

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/21798643



Change-Id: I073a9241805877aa6886b75f0e51c84428deacc8
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>