Merge "Document the expected value of volume control id parameter" into udc-dev am: ec281057

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/22380604



Change-Id: I85f59862857715398971d7805bd771656754e40a
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>