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This is a reland of 916c54c5

Original change's description:
> Add browsertests for tab sharing UI views.
>
> Add tests to verify tab sharing UI elements: infobars, contents border
> and tab sharing indicator.
>
> Bug: 996722
> Change-Id: I5fa5ec7e4a48a66c1ba9b08ff76b84a105961352
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1847287
> Reviewed-by: Guido Urdaneta <guidou@chromium.org>
> Commit-Queue: Marina Ciocea <marinaciocea@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#707368}

Bug: 996722
Change-Id: Ic325cb95314cbe299253895f15534a83ef8b193e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1878409Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Commit-Queue: Marina Ciocea <marinaciocea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#709017}