Handle audio device changes on Windows.

media/audio/win/audio_device_listener_win.h

Index: media/audio/win/audio_device_listener_win.h
diff --git a/media/audio/win/audio_device_listener_win.h b/media/audio/win/audio_device_listener_win.h
new file mode 100644
index 0000000000000000000000000000000000000000..d2c38b39353f3d20d8b35649b41bf9306b6f2eca
--- /dev/null
+++ b/media/audio/win/audio_device_listener_win.h
@@ -0,0 +1,62 @@
+// 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_WIN_AUDIO_DEVICE_LISTENER_WIN_H_
+#define MEDIA_AUDIO_WIN_AUDIO_DEVICE_LISTENER_WIN_H_
+
+#include <MMDeviceAPI.h>
+#include <string>
+
+#include "base/basictypes.h"
+#include "base/callback.h"
+#include "base/threading/thread_checker.h"
+#include "base/win/scoped_comptr.h"
+#include "media/base/media_export.h"
+
+using base::win::ScopedComPtr;
+
+namespace media {
+
+// IMMNotificationClient implementation for listening for default device changes
+// and forwarding to AudioManagerWin so it can notify downstream clients.  Only
+// output (eRender) device changes are supported currently.  WASAPI support is
+// required to construct this object.  Must be constructed and destructed on a
+// single COM initialized thread.
+// TODO(henrika): Refactor based on upcoming CoreAudioUtil class for windows.
+// TODO(dalecurtis, henrika): Support input device changes.
+class MEDIA_EXPORT AudioDeviceListenerWin : public IMMNotificationClient {
+ public:
+  // The listener callback will be called from a system level multimedia thread,
+  // thus the callee must be thread safe.  |listener| is a permanent callback
+  // and must outlive AudioDeviceListenerWin.
+  explicit AudioDeviceListenerWin(const base::Closure& listener_cb);
+  virtual ~AudioDeviceListenerWin();
+
+ private:
+  friend class AudioDeviceListenerWinTest;
+
+  // IMMNotificationClient implementation.
+  STDMETHOD_(ULONG, AddRef)();
+  STDMETHOD_(ULONG, Release)();
+  STDMETHOD(QueryInterface)(REFIID iid, void** object);
+  STDMETHOD(OnPropertyValueChanged)(LPCWSTR device_id, const PROPERTYKEY key);
+  STDMETHOD(OnDeviceAdded)(LPCWSTR device_id);
+  STDMETHOD(OnDeviceRemoved)(LPCWSTR device_id);
+  STDMETHOD(OnDeviceStateChanged)(LPCWSTR device_id, DWORD new_state);
+  STDMETHOD(OnDefaultDeviceChanged)(EDataFlow flow, ERole role,
+                                    LPCWSTR new_default_device_id);
+
+  base::Closure listener_cb_;
+  ScopedComPtr<IMMDeviceEnumerator> device_enumerator_;
+  std::string default_render_device_id_;
+
+  // AudioDeviceListenerWin must be constructed and destructed on one thread.
+  base::ThreadChecker thread_checker_;
+
+  DISALLOW_COPY_AND_ASSIGN(AudioDeviceListenerWin);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_AUDIO_WIN_AUDIO_DEVICE_LISTENER_WIN_H_