R=clemensh@chromium.org

Bug: v8:6959
Change-Id: I27164598dddf58da7f3040b7139c4ae99c52800f
Reviewed-on: https://chromium-review.googlesource.com/733097Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48836}