Add BigInt to the list of allowed result types.

Bug: v8:6791, chromium:819871
Change-Id: Ib636859da07b38c462ce7017d720e5370ba618d6
Reviewed-on: https://chromium-review.googlesource.com/957422Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51859}