Since the code around that is quite fragile, and I plan to refactor it,
just add some tests to ensure that everything is and keeps working as
intended.

R=mstarzinger@chromium.org

Bug: v8:7758
Change-Id: Ib3814b93b465286d70b5669ed0161eecb9fc925a
Reviewed-on: https://chromium-review.googlesource.com/1059616Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53187}