Merge "Update volume behavior documentation." into udc-dev am: 2c351648

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/21518487



Change-Id: I92b7f3de30f16408d278059e6454a54b99010a16
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>