Add basic support for "googDucking" to getUserMedia on Windows.

media/audio/audio_parameters.h

 // 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_AUDIO_PARAMETERS_H_
 #define MEDIA_AUDIO_AUDIO_PARAMETERS_H_
 
 #include "base/basictypes.h"
 #include "base/time/time.h"
 #include "media/base/channel_layout.h"
@@ skipping 30 matching lines @@
     // Telephone quality sample rate, mostly for speech-only audio.
     kTelephoneSampleRate = 8000,
     // CD sampling rate is 44.1 KHz or conveniently 2x2x3x3x5x5x7x7.
     kAudioCDSampleRate = 44100,
   };
 
   // Bitmasks to determine whether certain platform (typically hardware) audio
   // effects should be enabled.
   enum PlatformEffectsMask {
     NO_EFFECTS = 0x0,
-    ECHO_CANCELLER = 0x1
+    ECHO_CANCELLER = 0x1,
+    DUCKING = 0x2,  // Enables ducking if the OS supports it.
   };
 
   AudioParameters();
   AudioParameters(Format format, ChannelLayout channel_layout,
                   int sample_rate, int bits_per_sample,
                   int frames_per_buffer);
   AudioParameters(Format format, ChannelLayout channel_layout,
                   int input_channels,
                   int sample_rate, int bits_per_sample,
                   int frames_per_buffer, int effects);
@@ skipping 73 matching lines @@
   if (a.sample_rate() != b.sample_rate())
     return a.sample_rate() < b.sample_rate();
   if (a.bits_per_sample() != b.bits_per_sample())
     return a.bits_per_sample() < b.bits_per_sample();
   return a.frames_per_buffer() < b.frames_per_buffer();
 }
 
 }  // namespace media
 
 #endif  // MEDIA_AUDIO_AUDIO_PARAMETERS_H_