Allow content_browser to access multizone

Just as media_service currently can access the multizone service, we are
adding this capability to the content_browser service.
CastAudioOutputStream runs in content_browser and requires this.

TEST=Build, play to MZ group through CastAudioOutputStream

Change-Id: I1ffad39d6c61a457f516960228e546462581bef6
Reviewed-by: Daniel Cheng <>
Reviewed-by: Ken Rockot <>
Commit-Queue: Aidan Wolter <>
Cr-Commit-Position: refs/heads/master@{#575845}
1 file changed