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This CL adds a secondary_title field to media_router.mojom.MediaStatus,
corresponding to the media.metadata.subtitle field in Cast SDK media
status messages, which contains artist names for media.

The artist name is shown in a Cast notification item in Global Media
Controls. Other labels are also rearranged to match the mocks.

Screenshot:
https://drive.google.com/file/d/1Ecr-7WsGFE7Be3MuPvsau3SEUwKPQPJr/view?usp=sharing

Bug: 1042016
Change-Id: Iff3cc50af41ef24e6a4e8ec10090acbffe049f8f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2003388
Commit-Queue: Takumi Fujimoto <takumif@chromium.org>
Reviewed-by: Tommy Steimel <steimel@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: mark a. foltz <mfoltz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#732551}