See MediaSessionCompat.Callback.onCommand(String, Bundle, ResultReceiver). The
receiver may handle the command, but is not required to do so. Changes to the player should
be made via the ControlDispatcher.
player - The player connected to the media session.
controlDispatcher - A ControlDispatcher that should be used for dispatching
changes to the player.
command - The command name.
extras - Optional parameters for the command, may be null.
cb - A result receiver to which a result may be sent by the command, may be null.