Use VoiceChannel/VideoChannel directly from RtpSender/RtpReceiver.

webrtc/api/rtpreceiverinterface.h

Index: webrtc/api/rtpreceiverinterface.h
diff --git a/webrtc/api/rtpreceiverinterface.h b/webrtc/api/rtpreceiverinterface.h
index 49888381e1cbd81027ce8112d5694ee34721330e..d15e08a996dc2c19f85f6ac1e554336b63f3d0a8 100644
--- a/webrtc/api/rtpreceiverinterface.h
+++ b/webrtc/api/rtpreceiverinterface.h
@@ -18,8 +18,10 @@
 
 #include "webrtc/api/mediastreaminterface.h"
 #include "webrtc/api/proxy.h"
+#include "webrtc/api/rtpparameters.h"
 #include "webrtc/base/refcount.h"
 #include "webrtc/base/scoped_ref_ptr.h"
+#include "webrtc/pc/mediasession.h"
 
 namespace webrtc {
 
@@ -27,6 +29,9 @@ class RtpReceiverInterface : public rtc::RefCountInterface {
  public:
   virtual rtc::scoped_refptr<MediaStreamTrackInterface> track() const = 0;
 
+  // Audio or video receiver?
+  virtual cricket::MediaType media_type() const = 0;
+
   // Not to be confused with "mid", this is a field we can temporarily use
   // to uniquely identify a receiver until we implement Unified Plan SDP.
   virtual std::string id() const = 0;
@@ -44,6 +49,7 @@ class RtpReceiverInterface : public rtc::RefCountInterface {
 // Define proxy for RtpReceiverInterface.
 BEGIN_SIGNALING_PROXY_MAP(RtpReceiver)
 PROXY_CONSTMETHOD0(rtc::scoped_refptr<MediaStreamTrackInterface>, track)
+PROXY_CONSTMETHOD0(cricket::MediaType, media_type)
 PROXY_CONSTMETHOD0(std::string, id)
 PROXY_CONSTMETHOD0(RtpParameters, GetParameters);
 PROXY_METHOD1(bool, SetParameters, const RtpParameters&)