R=titzer@chromium.org

Bug: 
Change-Id: Ib1a13b5131ec1b5a155c893de3c5ceb376bd33a3
Reviewed-on: https://chromium-review.googlesource.com/600227
Commit-Queue: Andreas Rossberg <rossberg@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47139}