Adding microphone volume support to chrome.

media/audio/mac/audio_low_latency_input_mac.h

Index: media/audio/mac/audio_low_latency_input_mac.h
diff --git a/media/audio/mac/audio_low_latency_input_mac.h b/media/audio/mac/audio_low_latency_input_mac.h
index 6b5c720345b18383332463b06e8858217d921ead..537eeb434b1bce9b9a0a0f9eb0f93168cc8c30a1 100644
--- a/media/audio/mac/audio_low_latency_input_mac.h
+++ b/media/audio/mac/audio_low_latency_input_mac.h
@@ -29,7 +29,7 @@
 // - Calling Close() also leads to self destruction.
 // - The latency consists of two parts:
 //   1) Hardware latency, which includes Audio Unit latency, audio device
-//      latency;
+//      latency and audio stream latency;
 //   2) The delay between the actual recording instant and the time when the
 //      data packet is provided as a callback.
 //
@@ -61,6 +61,9 @@ class AUAudioInputStream : public AudioInputStream {
   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;
 
   // Returns the current hardware sample rate for the default input device.
   static double HardwareSampleRate();
@@ -89,9 +92,16 @@ class AUAudioInputStream : public AudioInputStream {
   // Gets the current capture delay value.
   double GetCaptureLatency(const AudioTimeStamp* input_time_stamp);
 
+  // Gets the number of channels for a stream of audio data.
+  UInt32 GetNumberOfChannelsFromStream();
+
   // Issues the OnError() callback to the |sink_|.
   void HandleError(OSStatus err);
 
+  // Helper function to check if the volume control is avialable on specific
+  // channel.
+  bool IsVolumeSettableOnChannel(int channel);
+
   // Our creator, the audio manager needs to be notified when we close.
   AudioManagerMac* manager_;
 
@@ -126,6 +136,10 @@ class AUAudioInputStream : public AudioInputStream {
   // Fixed capture hardware latency in frames.
   double hardware_latency_frames_;
 
+  // The number of channels in each frame of audio data, which is used
+  // when querying the volume of each channel.
+  UInt32 number_of_channels_in_frame_;
+
   DISALLOW_COPY_AND_ASSIGN(AUAudioInputStream);
 };