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 4943023111b5b4261baecdab6d23e9d9bb7d974e..53a37398cfc9222c6c6528640920fb619d728a1f 100644
--- a/webrtc/api/rtpreceiverinterface.h
+++ b/webrtc/api/rtpreceiverinterface.h
@@ -18,6 +18,7 @@
 
 #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"
@@ -26,6 +27,12 @@ namespace webrtc {
 
 class RtpReceiverObserverInterface {
  public:
+  // Note: Currently if there are multiple RtpReceivers of the same media type,
+  // they will all call OnFirstPacketReceived at once.
+  //
+  // In the future, it's likely that an RtpReceiver will only call
+  // OnFirstPacketReceived when a packet is received specifically for its
+  // SSRC/mid.
   virtual void OnFirstPacketReceived(cricket::MediaType media_type) = 0;
 
  protected:
@@ -36,6 +43,9 @@ 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;
@@ -46,10 +56,10 @@ class RtpReceiverInterface : public rtc::RefCountInterface {
   virtual RtpParameters GetParameters() const = 0;
   virtual bool SetParameters(const RtpParameters& parameters) = 0;
 
+  // Does not take ownership of observer.
+  // Must call SetObserver(nullptr) before the observer is destroyed.
   virtual void SetObserver(RtpReceiverObserverInterface* observer) = 0;
 
-  virtual cricket::MediaType media_type() = 0;
-
  protected:
   virtual ~RtpReceiverInterface() {}
 };
@@ -57,11 +67,11 @@ 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&)
 PROXY_METHOD1(void, SetObserver, RtpReceiverObserverInterface*);
-PROXY_METHOD0(cricket::MediaType, media_type);
 END_SIGNALING_PROXY()
 
 }  // namespace webrtc