[Chromoting] Move DefaultAudioDeviceChangeDetector out of AudioCapturerWin

remoting/host/win/default_audio_device_change_detector.h

+// Copyright 2017 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 REMOTING_HOST_WIN_DEFAULT_AUDIO_DEVICE_CHANGE_DETECTOR_H_
+#define REMOTING_HOST_WIN_DEFAULT_AUDIO_DEVICE_CHANGE_DETECTOR_H_
+
+#include <mmdeviceapi.h>
+
+#include "base/synchronization/lock.h"
+#include "base/win/scoped_comptr.h"
+
+namespace remoting {
+
+// An IMMNotificationClient implementation to detect the change of the default
+// audio output device on the system. It registers itself into the input
+// IMMDeviceEnumerator in constructor, and unregisters in destructor.

[joedow, 2017/04/24 17:29:41]

nit: remove comma

[Hzj_jie, 2017/04/24 22:45:02]

Done.

+// This class does not use the default referring memory management method

[joedow, 2017/04/24 17:29:41]

s/referring/ref-counting

[Hzj_jie, 2017/04/24 22:45:02]

Done.

+// provided by IUnknown: calling DefaultAudioDeviceChangeDetector::Release()
+// won't delete the object.
+class DefaultAudioDeviceChangeDetector final : public IMMNotificationClient {
+ public:
+  DefaultAudioDeviceChangeDetector(
+      const base::win::ScopedComPtr<IMMDeviceEnumerator>& enumerator);

[joedow, 2017/04/24 17:29:41]

single param c'tors should be marked explicit

[Hzj_jie, 2017/04/24 22:45:02]

Done.

+  ~DefaultAudioDeviceChangeDetector();

[joedow, 2017/04/24 17:29:41]

override?

[Hzj_jie, 2017/04/24 22:45:02]

e:\b\c\b\win\src\remoting\host\win\default_audio_device_change_detector.h(25):
error C3668:
'remoting::DefaultAudioDeviceChangeDetector::~DefaultAudioDeviceChangeDetector':
method with override specifier 'override' did not override any base class
methods

It looks like IMMNotificationClient does not have a destructor at all.

+
+  bool GetAndReset();
+
+ private:
+  HRESULT __stdcall OnDefaultDeviceChanged(EDataFlow flow,
+                                           ERole role,
+                                           LPCWSTR pwstrDefaultDevice) override;
+
+  HRESULT __stdcall QueryInterface(REFIID iid, void** object) override;
+
+  // No-ops overrides.

[joedow, 2017/04/24 17:29:41]

I wouldn't call out the no-op bit here, just document the methods:
// IMMNotificationClient implementation.

[Hzj_jie, 2017/04/24 22:45:02]

I think both comments should be useful here. No-ops overrides can tell the
readers only the two functions above are relative.

+  HRESULT __stdcall OnDeviceAdded(LPCWSTR pwstrDeviceId) override;
+  HRESULT __stdcall OnDeviceRemoved(LPCWSTR pwstrDeviceId) override;
+  HRESULT __stdcall OnDeviceStateChanged(LPCWSTR pwstrDeviceId,
+                                         DWORD dwNewState) override;
+  HRESULT __stdcall OnPropertyValueChanged(LPCWSTR pwstrDeviceId,
+                                           const PROPERTYKEY key) override;
+  ULONG __stdcall AddRef() override;
+  ULONG __stdcall Release() override;
+
+  const base::win::ScopedComPtr<IMMDeviceEnumerator> enumerator_;
+  bool changed_ = false;
+  base::Lock lock_;
+};
+
+}  // namespace remoting
+
+#endif  // REMOTING_HOST_WIN_DEFAULT_AUDIO_DEVICE_CHANGE_DETECTOR_H_