R=titzer@chromium.org

Change-Id: Ie8c361efb48b56dc65719f09dfc79d505e0f3459
Reviewed-on: https://chromium-review.googlesource.com/735610
Commit-Queue: Andreas Rossberg <rossberg@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49000}