This reverts commit 4a2b2b2e.

Reason for revert: Speculative revert due to https://ci.chromium.org/p/chromium/builders/try/linux-rel/495075?

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}

TBR=ulan@chromium.org,etiennep@chromium.org

Change-Id: I63f24bffa0f56c6ffa1d1977fc4fb8a76b6f3ba2
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2423722Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Commit-Queue: Nico Hartmann <nicohartmann@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70049}