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This is a reland of 278cb45f

Original change's description:
> Video Tutorials: Added video player UI
>
> This CL adds the video player UI.
> 1 - Added VideoPlayerActivity at chrome layer, which creates
> VideoPlayerCoordinator and passes a WebContent supplier in order to
> create ThinWebView.
> 2 - Added video player MVC, the mediator handles display logic between
> loading screen, controls, thinwebview, and language picker.
> It also handles callbacks for control buttons, and observes media
> session through a PlaybackStateObserver.
>
> TODO :
> Add screenshot. Add UI polish. Define share/watchnext behavior.
> Polish media session logic.
>
> Bug: 1117172
> Binary-Size: Unavoidable method count increase (includes methods from previous CL).
> Change-Id: Ide7c0d7bf4fa20a9bfbe0c10717e6983d0da88dc
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2415672
> Commit-Queue: Shakti Sahu <shaktisahu@chromium.org>
> Reviewed-by: David Trainor <dtrainor@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#811094}

TBR=dtrainor@chromium.org

Bug: 1117172
Change-Id: If6c7fd26ba1643ded722eb274f876dad085dd075
Binary-Size: Unavoidable method count increase (includes methods from previous CL).
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2434560Reviewed-by: Shakti Sahu <shaktisahu@chromium.org>
Commit-Queue: Shakti Sahu <shaktisahu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811112}