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This is a reland of 9771027b

Original change's description:
> desks: Fix crash when touchpad swipe with external monitors.
>
> The crash was because a new screenshot is requested when the current
> screenshot is about to get scrolled out of bounds. It was using a fixed
> number threshold, meaning displays that are not the same size could
> get out of sync easily, leading to a CHECK failure.
>
> This CL addresses that by requesting screenshot on all displays if even
> one of them needs one. Another approach would be change the spacing and
> threshold to be based on the display width instead of fixed number, but
> that could be prone to roundoff error which may cause a similar issue.
>
> Also noticed visible desk metric was double counting when there are
> multiple displays. Added a TODO for that one as it is lower priority.
>
> Bug: 1154868
> Test: manual, added regression test
> Change-Id: I48f5ef62d3284b710f44a2808f75c95686bc9b3d
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2570551
> Commit-Queue: Sammie Quon <sammiequon@chromium.org>
> Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#833993}

Bug: 1154868
Change-Id: Ib5a1fdd6b5778d350931663862c3204b1bab34fc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2575850Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#834520}