It is possible for 2 different threads to poke the mStreamControls at the same time,
causing the monkey bug mentioned in the bug report below.
Bug: 6411852
Couldn't think of any other reason Stream type 3 (MUSIC) wouldn't exist in the list.
It's possible that a programmatic call came in at the same time as the volume key press.
Synchronizing blocks where the mStreamControls are populated and accessed.
Change-Id: Ifedec6b0f8bad9634cb9e079fda785c433bdb7a7
a654986978