Set media router group id to sync cast status

Using media router group id, Settings can sync cast status with
Settings.
If Settings begins/stops cast (mirrorring), CastTile can know that and
Settings also knows when CastTile begins cast.

Please refer ag/7669852 to how router group id can be used to
synchronize cast status.

Bug: 112826114
Bug: 131385091
Bug: 130345243

Test: Manually tested after applying ag/7704172 and this.
Change-Id: I78c3c6163e1352b3a8d0801890064369a861fb8a