R=rossberg@chromium.org

Bug: chromium:772636
Change-Id: I885f8657eb755953be17d7bf32aef2629092b9c2
Reviewed-on: https://chromium-review.googlesource.com/733086Reviewed-by: Andreas Rossberg <rossberg@chromium.org>
Commit-Queue: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48830}