Reland "[media_preview] Add tests for VideoStreamCoordinator metrics"

This is a reland of commit 91cf594e

The original submit was interleaved with a submit that change the
mojo API for VideoSource. This reland updates the impl to match.

Original change's description:
> [media_preview] Add tests for VideoStreamCoordinator metrics
>
> This covers PixelHeight, ExpectedFPS, ActualFPS,
> RenderedPercent.
>
> Fixed: b:329663133, b:329664065, b:329664520, b:330394977
> Change-Id: Ida86331e0959718218e5526d1e7a31de42b1684b
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5401460


> Reviewed-by: Ahmed Moussa <ahmedmoussa@google.com>
> Commit-Queue: Bryant Chandler <bryantchandler@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1282717}

Change-Id: Ic59b7174cff24ae548aabf6949a1365d01f61466
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5426062


Reviewed-by: Ahmed Moussa <ahmedmoussa@google.com>
Commit-Queue: Bryant Chandler <bryantchandler@chromium.org>
Cr-Commit-Position: refs/heads/main@{#12828009}