R=titzer@chromium.org

Bug: v8:6647
Change-Id: I73f19111b5c40988d57e9086852da902ba36acb2
Reviewed-on: https://chromium-review.googlesource.com/599872Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Andreas Rossberg <rossberg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47128}