Adding microphone volume support to chrome.

media/audio/linux/alsa_util.h

 // Copyright (c) 2010 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_LINUX_ALSA_UTIL_H_
 #define MEDIA_AUDIO_LINUX_ALSA_UTIL_H_
 
 #include <alsa/asoundlib.h>
+#include <string>
 
 class AlsaWrapper;
 
 namespace alsa_util {
 
 snd_pcm_format_t BitsToFormat(int bits_per_sample);
 
 snd_pcm_t* OpenCaptureDevice(AlsaWrapper* wrapper,
                              const char* device_name,
                              int channels,
                              int sample_rate,
                              snd_pcm_format_t pcm_format,
                              int latency_us);
 
 snd_pcm_t* OpenPlaybackDevice(AlsaWrapper* wrapper,
                               const char* device_name,
                               int channels,
                               int sample_rate,
                               snd_pcm_format_t pcm_format,
                               int latency_us);
 
 int CloseDevice(AlsaWrapper* wrapper, snd_pcm_t* handle);
 
+snd_mixer_t* OpenMixer(AlsaWrapper* wrapper, const std::string& device_name);
+
+void CloseMixer(AlsaWrapper* wrapper,
+                snd_mixer_t* mixer,
+                const std::string& device_name);
+
+snd_mixer_elem_t* LoadCaptureMixerElement(AlsaWrapper* wrapper,
+                                          snd_mixer_t* mixer);
+
 }
 
 #endif  // MEDIA_AUDIO_LINUX_ALSA_UTIL_H_