Cleanup AudioDeviceThread to avoid accidental misuse.

content/browser/audio_manager_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_MANAGER_THREAD_H_
+#define CONTENT_BROWSER_AUDIO_MANAGER_THREAD_H_
+
+#include "base/memory/ref_counted.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
+// AudioManagerThread was constructed on.
+class CONTENT_EXPORT AudioManagerThread {
+ public:
+  // Constructs and starts a thread. On all platforms except for Mac, the
+  // started thread becomes the audio task runner. However, on Mac, the task
+  // runner this object is constructed on will become the audio thread and the
+  // thread is only used for high complexity tasks which can't be run on the
+  // main thread (typically the UI thread).
+  AudioManagerThread();
+  ~AudioManagerThread();
+
+  scoped_refptr<base::SingleThreadTaskRunner> task_runner() const {
+    return task_runner_;
+  };
+
+  scoped_refptr<base::SingleThreadTaskRunner> worker_task_runner() const {
+    return thread_.task_runner();
+  }
+
+ private:
+  base::Thread thread_;
+
+  // Task runner to run audio control calls on.
+  scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
+
+  DISALLOW_COPY_AND_ASSIGN(AudioManagerThread);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_AUDIO_MANAGER_THREAD_H_