Merge "Trigger background memory trim when SystemUI is idle" into udc-dev am: d516a7ca am: 92b445bd am: 7ac3952a am: ec6adfaa

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/23130319



Change-Id: I9ce12ef101a3c9eec9be141d22889d98e9f600f9
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>