Merge "Fetch active notifications on a background thread." into tm-dev am: 963615c7

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/17474951



Change-Id: I6377755f5a71f84a7572721a41514337aa9c2cf2
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>