Support external audio mixer in webrtc 2.

webrtc/api/peerconnectioninterface.h

Index: webrtc/api/peerconnectioninterface.h
diff --git a/webrtc/api/peerconnectioninterface.h b/webrtc/api/peerconnectioninterface.h
index 29badbd8bb6f8bdc687d8cbe6933adf87ee4a452..d4daf2435e3ac7de78092579413fbc4aa41bd7dc 100644
--- a/webrtc/api/peerconnectioninterface.h
+++ b/webrtc/api/peerconnectioninterface.h
@@ -87,6 +87,7 @@ class WebRtcVideoEncoderFactory;
 
 namespace webrtc {
 class AudioDeviceModule;
+class AudioMixer;
 class MediaConstraintsInterface;
 
 // MediaStream container interface.
@@ -803,6 +804,20 @@ rtc::scoped_refptr<PeerConnectionFactoryInterface> CreatePeerConnectionFactory(
     cricket::WebRtcVideoEncoderFactory* encoder_factory,
     cricket::WebRtcVideoDecoderFactory* decoder_factory);
 
+// Create a new instance of PeerConnectionFactoryInterface with external audio
+// mixer.
+//
+// If |audio_mixer| is null, an internal audio mixer will be created and used.
+rtc::scoped_refptr<PeerConnectionFactoryInterface>
+CreatePeerConnectionFactoryWithAudioMixer(
+    rtc::Thread* network_thread,
+    rtc::Thread* worker_thread,
+    rtc::Thread* signaling_thread,
+    AudioDeviceModule* default_adm,
+    cricket::WebRtcVideoEncoderFactory* encoder_factory,
+    cricket::WebRtcVideoDecoderFactory* decoder_factory,
+    rtc::scoped_refptr<AudioMixer> audio_mixer);
+
 // Create a new instance of PeerConnectionFactoryInterface.
 // Same thread is used as worker and network thread.
 inline rtc::scoped_refptr<PeerConnectionFactoryInterface>