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This is a reland of 7d2d8cc1

Original change's description:
> GMC: Redesign audio picker UI
> 
> Implement the new UI for the audio device picker in global media
> controls. As part of this change, the MediaNotificationBackground will
> draw a gradient between the device picker and notification artwork if
> the picker is availabile.
> 
> Screenshots of this updated UI will be posted on the crbug.
> 
> Change-Id: Ic7186c770102663b08e85b56eeddfbfa13833c3c
> Bug: 1117160
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2358512
> Commit-Queue: Noah Rose Ledesma <noahrose@google.com>
> Reviewed-by: Tommy Steimel <steimel@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#800243}

Bug: 1117160
Change-Id: I3adf5e58dcb8cd77758abd75aa5d497ab0f50c2a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2368504Reviewed-by: Tommy Steimel <steimel@chromium.org>
Commit-Queue: Noah Rose Ledesma <noahrose@google.com>
Cr-Commit-Position: refs/heads/master@{#800781}