When an audio track is disabled, still pass the data to webrtc for audio processing.

content/renderer/media/webrtc_local_audio_track.cc

Index: content/renderer/media/webrtc_local_audio_track.cc
diff --git a/content/renderer/media/webrtc_local_audio_track.cc b/content/renderer/media/webrtc_local_audio_track.cc
index 37846335e8531270c5c6c66658c400137b82bcf4..ce227367daecac8ac9c8abac4842fa023ae9f54c 100644
--- a/content/renderer/media/webrtc_local_audio_track.cc
+++ b/content/renderer/media/webrtc_local_audio_track.cc
@@ -159,8 +159,9 @@ void WebRtcLocalAudioTrack::Capture(media::AudioBus* audio_source,
     // When the track is disabled, we simply return here.
     // TODO(xians): Figure out if we should feed zero to sinks instead, in
     // order to inject VAD data in such case.
-    if (!enabled())
-      return;
+    if (!enabled()) {

[no longer working on chromium, 2013/09/27 12:31:52]

remove this if check

+      volume = 0;

[no longer working on chromium, 2013/09/26 20:52:31]

This is wrong, it will confuse the APM that the current analog volume is 0, then
APM will set the microphone volume to a value closed to 0. 

+    }
 
     capturer = capturer_;
     voe_channels = voe_channels_;