Adding microphone volume support to chrome.

media/audio/linux/alsa_input.h

 // Copyright (c) 2011 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_INPUT_H_
 #define MEDIA_AUDIO_LINUX_ALSA_INPUT_H_
 
 #include <alsa/asoundlib.h>
 
 #include <string>
@@ skipping 18 matching lines @@
 
   // Create a PCM Output stream for the ALSA device identified by
   // |device_name|. If unsure of what to use for |device_name|, use
   // |kAutoSelectDevice|.
   AlsaPcmInputStream(AudioManagerLinux* audio_manager,
                      const std::string& device_name,
                      const AudioParameters& params,
                      AlsaWrapper* wrapper);
   virtual ~AlsaPcmInputStream();
 
-  // Implementation of AudioOutputStream.
+  // Implementation of AudioInputStream.
   virtual bool Open() OVERRIDE;
   virtual void Start(AudioInputCallback* callback) OVERRIDE;
   virtual void Stop() OVERRIDE;
   virtual void Close() OVERRIDE;
+  virtual double GetMaxVolume() OVERRIDE;
+  virtual void SetVolume(double volume) OVERRIDE;
+  virtual double GetVolume() OVERRIDE;
 
  private:
   // Logs the error and invokes any registered callbacks.
   void HandleError(const char* method, int error);
 
   // Reads one or more packets of audio from the device, passes on to the
   // registered callback and schedules the next read.
   void ReadAudio();
 
   // Recovers from any device errors if possible.
   bool Recover(int error);
 
   // Utility function for talking with the ALSA API.
   snd_pcm_sframes_t GetCurrentDelay();
 
   // Non-refcounted pointer back to the audio manager.
   // The AudioManager indirectly holds on to stream objects, so we don't
   // want circular references.  Additionally, stream objects live on the audio
   // thread, which is owned by the audio manager and we don't want to addref
   // the manager from that thread.
   AudioManagerLinux* audio_manager_;
   std::string device_name_;
   AudioParameters params_;
   int bytes_per_packet_;
   AlsaWrapper* wrapper_;
   int packet_duration_ms_;  // Length of each recorded packet in milliseconds.
   AudioInputCallback* callback_;  // Valid during a recording session.
   base::Time next_read_time_;  // Scheduled time for the next read callback.
   snd_pcm_t* device_handle_;  // Handle to the ALSA PCM recording device.
+  snd_mixer_t* mixer_handle_; // Handle to the ALSA microphone mixer.
+  snd_mixer_elem_t* mixer_element_handle_; // Handle to the capture element.
   base::WeakPtrFactory<AlsaPcmInputStream> weak_factory_;
   scoped_array<uint8> audio_packet_;  // Buffer used for reading audio data.
   bool read_callback_behind_schedule_;
 
   DISALLOW_COPY_AND_ASSIGN(AlsaPcmInputStream);
 };
 
 #endif  // MEDIA_AUDIO_LINUX_ALSA_INPUT_H_