Factor out AudioOutputDelegate from AudioRendererHost.

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> task_runner() {
+#if defined(OS_MACOSX)
+    // On Mac audio task runner must belong to the main thread.
+    // See http://crbug.com/158170.
+    return base::ThreadTaskRunnerHandle::Get();
+#else
+    return thread_.task_runner();
+#endif  // defined(OS_MACOSX)
+  }
+
+  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_