This CL also allows reusing slow case for API callbacks.

Bug: chromium:1201781
Change-Id: Ib5f81c510404060c888ba30c82357d6ed1a95cf5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2882809
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74470}