Support external audio mixer in webrtc 2.

webrtc/media/base/mediaengine.h

Index: webrtc/media/base/mediaengine.h
diff --git a/webrtc/media/base/mediaengine.h b/webrtc/media/base/mediaengine.h
index 5b7443b6f3988b00144e02cd2ca3f1c27bfa3275..debc171360dcc4feb068b4a9af213f0c14347d80 100644
--- a/webrtc/media/base/mediaengine.h
+++ b/webrtc/media/base/mediaengine.h
@@ -33,6 +33,7 @@
 
 namespace webrtc {
 class AudioDeviceModule;
+class AudioMixer;
 class Call;
 }
 
@@ -110,11 +111,11 @@ class MediaEngineFactory {
 template<class VOICE, class VIDEO>
 class CompositeMediaEngine : public MediaEngineInterface {
  public:
-  CompositeMediaEngine(
-      webrtc::AudioDeviceModule* adm,
-      const rtc::scoped_refptr<webrtc::AudioDecoderFactory>&
-          audio_decoder_factory)
-      : voice_(adm, audio_decoder_factory) {}
+  CompositeMediaEngine(webrtc::AudioDeviceModule* adm,
+                       const rtc::scoped_refptr<webrtc::AudioDecoderFactory>&
+                           audio_decoder_factory,
+                       rtc::scoped_refptr<webrtc::AudioMixer> audio_mixer)
+      : voice_(adm, audio_decoder_factory, audio_mixer) {}
   virtual ~CompositeMediaEngine() {}
   virtual bool Init() {
     video_.Init();