Handle audio device changes on Mac

media/audio/mac/audio_device_listener_mac.h

Index: media/audio/mac/audio_device_listener_mac.h
diff --git a/media/audio/mac/audio_device_listener_mac.h b/media/audio/mac/audio_device_listener_mac.h
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index 0000000000000000000000000000000000000000..32497a5c462485010eb4921bb57220cb97e8ce9d
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+++ b/media/audio/mac/audio_device_listener_mac.h
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+// Copyright (c) 2012 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 MEDIA_AUDIO_MAC_AUDIO_DEVICE_LISTENER_MAC_H_
+#define MEDIA_AUDIO_MAC_AUDIO_DEVICE_LISTENER_MAC_H_
+
+#include "base/callback.h"
+#include "base/gtest_prod_util.h"
+#include "base/threading/thread_checker.h"
+#include "media/base/media_export.h"
+
+namespace media {
+
+// Listens for default device changes and forwards them to AudioManagerMac so it
+// can notify downstream clients. Only output device changes are supported
+// currently.
+class MEDIA_EXPORT AudioDeviceListenerMac {
+ public:
+  // The listener callback may be called from a system level multimedia thread,
+  // thus the callee must be thread safe.  |listener_cb| is a permanent callback
+  // and must outlive AudioDeviceListenerMac.
+  explicit AudioDeviceListenerMac(const base::Closure& listener_cb);
+  ~AudioDeviceListenerMac();
+
+  // Callback for when an audio device changes.
+  void OnDefaultDeviceChanged();
+
+ private:
+  FRIEND_TEST_ALL_PREFIXES(AudioDeviceListenerMacTest, OutputDeviceChange);
+  base::Closure listener_cb_;
+  base::ThreadChecker thread_checker_;
+
+  DISALLOW_COPY_AND_ASSIGN(AudioDeviceListenerMac);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_AUDIO_MAC_AUDIO_DEVICE_LISTENER_MAC_H_