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

base/task_scheduler/scheduler_service_thread.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_SERVICE_THREAD_H_
-#define BASE_TASK_SCHEDULER_SERVICE_THREAD_H_
-
-#include <memory>
-
-#include "base/base_export.h"
-#include "base/macros.h"
-
-namespace base {
-namespace internal {
-
-class DelayedTaskManager;
-class SchedulerWorker;
-class TaskTracker;
-
-// A thread dedicated to performing Task Scheduler related work.
-class BASE_EXPORT SchedulerServiceThread {
- public:
-  ~SchedulerServiceThread();
-
-  // Creates a SchedulerServiceThread. |task_tracker| and |delayed_task_manager|
-  // are passed through to the underlying SchedulerWorker. Returns a nullptr on
-  // failure.
-  static std::unique_ptr<SchedulerServiceThread> Create(
-      TaskTracker* task_tracker, DelayedTaskManager* delayed_task_manager);
-
-  // Wakes the SchedulerServiceThread if it wasn't already awake. This also has
-  // the impact of updating the amount of time the thread sleeps for delayed
-  // tasks.
-  void WakeUp();
-
-  // Joins this SchedulerServiceThread. This can only be called once.
-  void JoinForTesting();
-
- private:
-  SchedulerServiceThread(std::unique_ptr<SchedulerWorker> worker);
-
-  const std::unique_ptr<SchedulerWorker> worker_;
-
-  DISALLOW_COPY_AND_ASSIGN(SchedulerServiceThread);
-};
-
-}  // namespace internal
-}  // namespace base
-
-#endif  // BASE_TASK_SCHEDULER_SERVICE_THREAD_H_