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This also adds the screenshot to the view.
https://hsv.googleplex.com/5993630915362816

Test classes for the view and mediator are also added.

Bug: 1034733
Change-Id: Iaadf3e32d87c31bf453c049b416fa2cd7bf6445f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2211050
Commit-Queue: Jeffrey Cohen <jeffreycohen@chromium.org>
Reviewed-by: Kristi Park <kristipark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#776167}