TaskScheduler: Replace the SchedulerServiceThread with a base::Thread.

base/task_scheduler/task_scheduler_impl.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_TASK_SCHEDULER_TASK_SCHEDULER_IMPL_H_
 #define BASE_TASK_SCHEDULER_TASK_SCHEDULER_IMPL_H_
 
 #include <stddef.h>
 
 #include <memory>
@@ skipping 61 matching lines @@
   void Initialize(
       const std::vector<SchedulerWorkerPoolParams>& worker_pool_params_vector);
 
   // Returns the worker pool that runs Tasks with |traits|.
   SchedulerWorkerPool* GetWorkerPoolForTraits(const TaskTraits& traits);
 
   // Callback invoked when a non-single-thread |sequence| isn't empty after a
   // worker pops a Task from it.
   void ReEnqueueSequenceCallback(scoped_refptr<Sequence> sequence);
 
-  // Callback invoked when the delayed run time is changed from the
-  // DelayedTaskManager.
-  void OnDelayedRunTimeUpdated();
-
   TaskTracker task_tracker_;
-  DelayedTaskManager delayed_task_manager_;
+  Thread service_thread_;
+  std::unique_ptr<DelayedTaskManager> delayed_task_manager_;
   const WorkerPoolIndexForTraitsCallback worker_pool_index_for_traits_callback_;
   std::vector<std::unique_ptr<SchedulerWorkerPoolImpl>> worker_pools_;
-  std::unique_ptr<SchedulerServiceThread> service_thread_;
 
 #if DCHECK_IS_ON()
   // Set once JoinForTesting() has returned.
   AtomicFlag join_for_testing_returned_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(TaskSchedulerImpl);
 };
 
 }  // namespace internal
 }  // namespace base
 
 #endif  // BASE_TASK_SCHEDULER_TASK_SCHEDULER_IMPL_H_