Merge "Keep track of two top wallpapers to improve the control over each." into udc-dev am: a54b7778 am: e18e68ff

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/22336602



Change-Id: I500e78919517c0b1f26567263fca79473b15078d
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>