Delegate kept task id around for longer than the worker is considered
active, thus breaking the task_id < num_worker garantee. The fix is to
adjust the delegate lifetime.

Change-Id: I9aabb1286d507c09bfe9be4fd4f810f232d6e6b9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2437005
Commit-Queue: Etienne Pierre-Doray <etiennep@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70207}