Add volume control for windows host

remoting/host/audio_capturer_win.h

Index: remoting/host/audio_capturer_win.h
diff --git a/remoting/host/audio_capturer_win.h b/remoting/host/audio_capturer_win.h
index de3c7953229704ee612ac08ff1d30385549d61cb..30f5dd9f2beff01866ddf88312580c354cccd760 100644
--- a/remoting/host/audio_capturer_win.h
+++ b/remoting/host/audio_capturer_win.h
@@ -33,6 +33,16 @@ class AudioCapturerWin : public AudioCapturer {
   // to the network.
   void DoCapture();
 
+  // Returns current volume setting of the host, in range [0.0, 1.0]. If the
+  // audio has been muted, this function returns 0. If Windows API returns error
+  // (such as audio device has been disabled or unpluged), this function ignores
+  // host volume setting, and returns 1.0.
+  float GetAudioLevel();

[joedow, 2016/03/04 16:46:10]

Neither of the new methods change internal state so they can be marked const.

[Sergey Ulanov, 2016/03/04 21:30:03]

Actually GetAudioLevel() doesn't even need to be a method - it can be a static
function. Move it out of this class?

[Hzj_jie, 2016/03/09 19:47:57]

GetAudioLevel uses audio_volume_, ScopedComPtr<ISimpleAudioVolume>. Both GetMute
and GetMasterVolume are not const declared according to MSDN.
(https://msdn.microsoft.com/en-us/library/windows/desktop/dd316535(v=vs.85).aspx,
https://msdn.microsoft.com/en-us/library/windows/desktop/dd316533(v=vs.85).aspx)

+
+  // Processes a series of samples, and executes callback if the packet is
+  // qualified to be sent to client.
+  void ProcessSamples(BYTE* data, UINT32 frames, DWORD flags);

[Sergey Ulanov, 2016/03/04 21:30:03]

BYTE, UINT32, DWORD are all windows specific types, and it's best to avoid using
them when possible, except when you call windows APIs. in this case it's better
to use uint8_t, size_t and int32_t 

[Hzj_jie, 2016/03/09 19:47:57]

Done.

+
   PacketCapturedCallback callback_;
 
   AudioPacket::SamplingRate sampling_rate_;
@@ -46,6 +56,7 @@ class AudioCapturerWin : public AudioCapturer {
   base::win::ScopedComPtr<IAudioCaptureClient> audio_capture_client_;
   base::win::ScopedComPtr<IAudioClient> audio_client_;
   base::win::ScopedComPtr<IMMDevice> mm_device_;
+  base::win::ScopedComPtr<ISimpleAudioVolume> audio_volume_;
 
   HRESULT last_capture_error_;