- JobHandle::IsCompleted()
- JobDelegate::GetTaskId()
- worker_count passed as argument to GetMaxConcurrency().
  Jobs implementation must call the new GetMaxConcurrency(), but Jobs
  users aren't migrated yet.

Bug: chromium:1114823
Change-Id: Ie09a8847d1cb884b1e388903370e49f33fa25a64
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2374308Reviewed-by: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Etienne Pierre-Doray <etiennep@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69683}