TaskScheduler: Make SchedulerWorkerThread own its delegate.

base/task_scheduler/scheduler_thread_pool.h

Index: base/task_scheduler/scheduler_thread_pool.h
diff --git a/base/task_scheduler/scheduler_thread_pool.h b/base/task_scheduler/scheduler_thread_pool.h
index baf2386c0dcb4b2a74d96af2b53288531f5e8698..6cbf6f47411c2b590c7a9d085775b9146273881e 100644
--- a/base/task_scheduler/scheduler_thread_pool.h
+++ b/base/task_scheduler/scheduler_thread_pool.h
@@ -90,11 +90,12 @@ class BASE_EXPORT SchedulerThreadPool : public SchedulerThreadPoolInterface {
  private:
   class SchedulerWorkerThreadDelegateImpl;
 
-  SchedulerThreadPool(const EnqueueSequenceCallback& enqueue_sequence_callback,
-                      TaskTracker* task_tracker,
+  SchedulerThreadPool(TaskTracker* task_tracker,
                       DelayedTaskManager* delayed_task_manager);
 
-  bool Initialize(ThreadPriority thread_priority, size_t max_threads);
+  bool Initialize(ThreadPriority thread_priority,
+                  size_t max_threads,
+                  const EnqueueSequenceCallback& enqueue_sequence_callback);
 
   // Wakes up the last thread from this thread pool to go idle, if any.
   void WakeUpOneThread();
@@ -129,9 +130,6 @@ class BASE_EXPORT SchedulerThreadPool : public SchedulerThreadPoolInterface {
   // Signaled once JoinForTesting() has returned.
   WaitableEvent join_for_testing_returned_;
 
-  // Delegate for all worker threads in this pool.
-  std::unique_ptr<SchedulerWorkerThread::Delegate> worker_thread_delegate_;
-
   TaskTracker* const task_tracker_;
   DelayedTaskManager* const delayed_task_manager_;