Extend MediaRouter.UserRouteInfo to enable setting playback
information, which includes volume. When the user route instance
has a RemoteControlClient, forward any playback information to it.
Enable specifying a callback to be notified of volume events
on the route.
Extend MediaRouter.RouteInfo to enable retrieving playback
information.
Update RemoteControlClient javadoc to reflect which parts of the
API are not intended to be made public.
Change-Id: I59d728eb61747af6c8c89d53f0faeb07940594c3
1357012968