This is a reland of 3f797636.
Last time it broke a skia test. The test has since been fixed
in https://crbug.com/1005388

Original change's description:
> Set core.trustctime=false during git checkout operations.
>
> This should be faster and more general than running
> `git index --refresh` over all git repositories we can find.
>
> See "Proposal: Setting core.trustctime=false on Chromium's bots"
> on infra-dev (linked to from bug 330461 comment 45).
>
> Bug: 330461,642711,746763,740301.
> Change-Id: I7c35cffa107d46d9cf98f0e3e813ef2ab98df5fc
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1809419
> Reviewed-by: Andrii Shyshkalov <tandrii@google.com>
> Commit-Queue: Nico Weber <thakis@chromium.org>

Recipe-Nontrivial-Roll: chromiumos
Bug: 330461, 642711, 746763, 740301.
Change-Id: I5d09a93689e53e4339bff7b1173df938aee73a4d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1810400
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Andrii Shyshkalov <tandrii@google.com>