An AudioPlaybackConfiguration contains an IPlayer
interface for system control of a player. It is not
exposed to non-system signature components.
AudioService, through PlaybackActivityMonitor, is monitoring
the death of the IPlayer so the matching player can get
unregistered in case it meets its maker.
Test: use vendor/google_toolbox/team/audio/cmds/ClPlaybackActivity
Bug: 30258418
Change-Id: Ibf3bceba91882ff16bffbf1219c55a1f89ccb13f
9dc22c227c