This is a reland of 4848de2a
Issue 1136405: non empty ephemeron list after FinishConcurrentMarking
Fix: COMPLETE_TASKS_FOR_TESTING Join()s instead of Cancel()
Issue: Failing TSAN failures
Fix: Safe to reland after
https://chromium-review.googlesource.com/c/v8/v8/+/2461726

Original change's description:
> Reland "[Heap]: Marking use Jobs."
>
> This is a reland of 4a2b2b2e
>
> Original change's description:
> > [Heap]: Marking use Jobs.
> >
> > StopRequest is removed in favor of:
> > COMPLETE_TASKS_FOR_TESTING -> JoinForTesting()
> > PREEMPT_TASKS -> Pause()
> > COMPLETE_ONGOING_TASKS now has the same behavior as PREEMPT_TASKS
> > - we should avoid waiting on the main thread as much as possible.
> >
> > Change-Id: Icceeb4f0c0fda2ed234b2f26fe308b11410fcfb7
> > Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2376166
> > Commit-Queue: Etienne Pierre-Doray <etiennep@chromium.org>
> > Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#70037}
>
> Change-Id: I386f619501ad07997278543868bc889a60afcc8b
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2423938
> Commit-Queue: Etienne Pierre-Doray <etiennep@chromium.org>
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#70387}

Bug: chromium:1136405
Change-Id: I511c3d1747ef79ed6e7066c9a5bba052f9d4cd37
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2458246
Commit-Queue: Etienne Pierre-Doray <etiennep@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70416}