Adds Analog Gain Control (AGC) to the WebRTC client.

media/audio/win/audio_low_latency_input_win.h

Index: media/audio/win/audio_low_latency_input_win.h
diff --git a/media/audio/win/audio_low_latency_input_win.h b/media/audio/win/audio_low_latency_input_win.h
index d34c025cb30388c4296eb889465a131ddcda60df..587237c46f4b3ca4c60ceb9d3155bc2299918832 100644
--- a/media/audio/win/audio_low_latency_input_win.h
+++ b/media/audio/win/audio_low_latency_input_win.h
@@ -65,10 +65,12 @@
 
 #include <string>
 
+#include "base/atomicops.h"
 #include "base/compiler_specific.h"
 #include "base/threading/non_thread_safe.h"
 #include "base/threading/platform_thread.h"
 #include "base/threading/simple_thread.h"
+#include "base/time.h"
 #include "base/win/scoped_co_mem.h"
 #include "base/win/scoped_com_initializer.h"
 #include "base/win/scoped_comptr.h"
@@ -102,6 +104,8 @@ class MEDIA_EXPORT WASAPIAudioInputStream
   virtual double GetMaxVolume() OVERRIDE;
   virtual void SetVolume(double volume) OVERRIDE;
   virtual double GetVolume() OVERRIDE;
+  virtual void SetAutomaticGainControl(bool enabled) OVERRIDE;
+  virtual bool GetAutomaticGainControl() OVERRIDE;
 
   // Retrieves the sample rate used by the audio engine for its internal
   // processing/mixing of shared-mode streams given a specifed device.
@@ -176,6 +180,19 @@ class MEDIA_EXPORT WASAPIAudioInputStream
   // Converts from milliseconds to audio frames.
   double ms_to_frame_count_;
 
+  // Keeps track of last time a new volume level was fed to the client in an
+  // OnData() callback.
+  base::Time last_volume_update_time_;
+
+  // Contains last result of internal call to GetVolume(). We save resources
+  // but not querying the capture volume for each callback.
+  double volume_;
+
+  // True when Automatic Gain Control is enabled, false otherwise.
+  // This member is modified on the audio thread and read on the internal
+  // WASAPI capture thread in each capture callback.
+  base::subtle::Atomic32 agc_is_enabled_;
+
   // Pointer to the object that will receive the recorded audio samples.
   AudioInputCallback* sink_;