In many cases, the event we are waiting for already happened. In that
case, entering the {ExecuteCompilationUnits} function creates
significant overhead.

This CL fixes this by just checking whether the event we are waiting for
already happened, and returning early in that case. This should restore
the original performance before https://crrev.com/c/2351671.

R=thibaudm@chromium.org

Bug: v8:10922
Change-Id: I5229808162a3b348bbbb067bd10065894c8a655c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2414028Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69976}