This factors out one part of the "Remove finisher task" CL
(https://crrev.com/c/1400781), which I would like to test in isolation.

R=ahaas@chromium.org

Bug: v8:8423
Change-Id: I7c598f60c4757df8e26508e68da4b3c300a511cb
Reviewed-on: https://chromium-review.googlesource.com/c/1448316Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59256}