This is more useful than always returning undefined.

BUG=v8:1569,v8:5978

Change-Id: Id10cf87f7865db1a85de412460eaead4e4bf3b62
Reviewed-on: https://chromium-review.googlesource.com/446846Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43498}