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

media/audio/mac/audio_input_mac.cc

Index: media/audio/mac/audio_input_mac.cc
diff --git a/media/audio/mac/audio_input_mac.cc b/media/audio/mac/audio_input_mac.cc
index 61ab281dadb22a18899607bd1cea9f4c0db9af1d..0277a00018eb01ffbaebff94bf4e6f3ca0cdb16f 100644
--- a/media/audio/mac/audio_input_mac.cc
+++ b/media/audio/mac/audio_input_mac.cc
@@ -127,6 +127,15 @@ double PCMQueueInAudioInputStream::GetVolume() {
   return 0.0;
 }
 
+void PCMQueueInAudioInputStream::SetAutomaticGainControl(bool enabled) {
+  NOTREACHED() << "Only supported for low-latency mode.";
+}
+
+bool PCMQueueInAudioInputStream::GetAutomaticGainControl() {
+  NOTREACHED() << "Only supported for low-latency mode.";
+  return false;
+}
+
 void PCMQueueInAudioInputStream::HandleError(OSStatus err) {
   if (callback_)
     callback_->OnError(this, static_cast<int>(err));
@@ -189,7 +198,8 @@ void PCMQueueInAudioInputStream::HandleInputBuffer(
     callback_->OnData(this,
                       reinterpret_cast<const uint8*>(audio_buffer->mAudioData),
                       audio_buffer->mAudioDataByteSize,
-                      audio_buffer->mAudioDataByteSize);
+                      audio_buffer->mAudioDataByteSize,
+                      0.0);
   // Recycle the buffer.
   OSStatus err = QueueNextBuffer(audio_buffer);
   if (err != noErr) {