Cleanup AudioDeviceThread to avoid accidental misuse.

content/browser/audio_device_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 CONTENT_BROWSER_AUDIO_DEVICE_THREAD_H_
-#define CONTENT_BROWSER_AUDIO_DEVICE_THREAD_H_
-
-#include "base/threading/thread.h"
-#include "content/common/content_export.h"
-
-namespace content {
-
-// This class encapulates the logic for the thread and task runners that the
-// AudioManager and related classes run on. audio_task_runner and
-// worker_task_runner should be called on the same thread as the
-// AudioDeviceThread was constructed on.
-class CONTENT_EXPORT AudioDeviceThread {
- public:
-  // Constructs and starts the thread.
-  AudioDeviceThread();
-
-  scoped_refptr<base::SingleThreadTaskRunner> GetTaskRunner();
-
-  scoped_refptr<base::SingleThreadTaskRunner> worker_task_runner() {
-    return thread_.task_runner();
-  }
-
- private:
-  base::Thread thread_;
-
-  DISALLOW_COPY_AND_ASSIGN(AudioDeviceThread);
-};
-
-}  // namespace content
-
-#endif  // CONTENT_BROWSER_AUDIO_DEVICE_THREAD_H_