[Jobs]: Fix task id lifetime.

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}

src/libplatform/default-job.h

@@ -127,9 +127,11 @@ class DefaultJobWorker : public Task {
   void Run() override {
     auto shared_state = state_.lock();
     if (!shared_state) return;
-    DefaultJobState::JobDelegate delegate(shared_state.get());
     if (!shared_state->CanRunFirstTask()) return;
     do {
+      // Scope of |delegate| must not outlive DidRunTask() so that associated
+      // state is freed before the worker becomes inactive.
+      DefaultJobState::JobDelegate delegate(shared_state.get());
       job_task_->Run(&delegate);
     } while (shared_state->DidRunTask());
   }