Added a kEchoCancellation constraint to turn off the audio processing.

content/renderer/media/webrtc_audio_capturer.cc

Index: content/renderer/media/webrtc_audio_capturer.cc
diff --git a/content/renderer/media/webrtc_audio_capturer.cc b/content/renderer/media/webrtc_audio_capturer.cc
index 482d25f1114b2479baabcda0d4fb930c4e5ba944..1548fd123b9c4a11984845a63a1943cc33a62f26 100644
--- a/content/renderer/media/webrtc_audio_capturer.cc
+++ b/content/renderer/media/webrtc_audio_capturer.cc
@@ -163,6 +163,13 @@ bool WebRtcAudioCapturer::Initialize() {
     return true;
   }
 
+  MediaAudioConstraints audio_constraints(constraints_,
+                                          device_info_.device.input.effects);
+  if (!audio_constraints.IsValid()) {

[no longer working on chromium, 2014/04/11 16:47:05]

Per, after thinking a bit more, I am not sure if we should check the mandatory
constraints. For example, if we are deprecating some of our goog* constraints,
and remove it from our code base, then our users putting those constraints to
mandatory filed will fail on AddTrack.

[perkj_chrome, 2014/04/14 12:15:19]

If they are mandatory, we should fail. But if that is not the behavior we
currently have with the goog prefixed, you can consider filtering them out and
only fail if its  a w3c defined constraint. 

+    DLOG(ERROR) << "Constraints contain invalid mandatory keys";
+    return false;
+  }
+
   media::ChannelLayout channel_layout = static_cast<media::ChannelLayout>(
       device_info_.device.input.channel_layout);
   DVLOG(1) << "Audio input hardware channel layout: " << channel_layout;
@@ -220,8 +227,7 @@ WebRtcAudioCapturer::WebRtcAudioCapturer(
     : constraints_(constraints),
       audio_processor_(
           new talk_base::RefCountedObject<MediaStreamAudioProcessor>(
-              constraints, device_info.device.input.effects,
-              device_info.device.type, audio_device)),
+              constraints, device_info.device.input.effects, audio_device)),
       running_(false),
       render_view_id_(render_view_id),
       device_info_(device_info),
@@ -320,8 +326,9 @@ void WebRtcAudioCapturer::SetCapturerSource(
     // Notify the |audio_processor_| of the new format.
     audio_processor_->OnCaptureFormatChanged(params);
 
-    need_audio_processing_ = NeedsAudioProcessing(
-        constraints_, device_info_.device.input.effects);
+    MediaAudioConstraints audio_constraints(constraints_,
+                                            device_info_.device.input.effects);
+    need_audio_processing_ = audio_constraints.NeedsAudioProcessing();
     // Notify all tracks about the new format.
     tracks_.TagAll();
   }