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Adds a unit test split out from https://crrev.com/c/1311080 (PS9)
Landing separately to make release branch merging easier.

Bug: 899084
Test: Automated
Change-Id: Icadd82f2490bc4f3bbbdd1c73f8cdbe584f03289
Reviewed-on: https://chromium-review.googlesource.com/c/1318363
Commit-Queue: Michael Wasserman <msw@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605623}