R=rossberg@chromium.org

Bug: 
Change-Id: I2401709b42106c7e325144b53be3c3b3d1ed16c7
Reviewed-on: https://chromium-review.googlesource.com/599874Reviewed-by: Andreas Rossberg <rossberg@chromium.org>
Commit-Queue: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47127}