Merge "Optimize attaching / detaching audio mixes." into udc-dev am: 12504654 am: 21b9fd35

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/22607657



Change-Id: I6b77327a44e2c0422734b89f6823b59a9d6e7d15
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>