This slows down promise benchmarks since we process all unhandled promises.

Bug: vu:1099632
Change-Id: I2188a2842ec0a69ca93e5d406f10371ceff60f9b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2270235Reviewed-by: Michael Stanton <mvstanton@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68575}