Create an Obj-C wrapper of the RtpReceiverObserverInterface.

webrtc/sdk/objc/Framework/Classes/RTCRtpReceiver+Private.h

Index: webrtc/sdk/objc/Framework/Classes/RTCRtpReceiver+Private.h
diff --git a/webrtc/sdk/objc/Framework/Classes/RTCRtpReceiver+Private.h b/webrtc/sdk/objc/Framework/Classes/RTCRtpReceiver+Private.h
index 14b68fa011384251d0afa6e79629fd3aa62db538..3dc0285d6b021324981ddd731b3c5062e3ad02ce 100644
--- a/webrtc/sdk/objc/Framework/Classes/RTCRtpReceiver+Private.h
+++ b/webrtc/sdk/objc/Framework/Classes/RTCRtpReceiver+Private.h
@@ -14,6 +14,20 @@
 
 NS_ASSUME_NONNULL_BEGIN
 
+namespace webrtc {
+
+class RtpReceiverDelegateAdapter : public RtpReceiverObserverInterface {
+ public:
+  RtpReceiverDelegateAdapter(RTCRtpReceiver* receiver);
+
+  void OnFirstPacketReceived(cricket::MediaType media_type) override;
+
+ private:
+  __weak RTCRtpReceiver* receiver_;
+};
+
+}  // namespace webrtc
+
 @interface RTCRtpReceiver ()
 
 @property(nonatomic, readonly)
@@ -24,6 +38,8 @@ NS_ASSUME_NONNULL_BEGIN
     (rtc::scoped_refptr<webrtc::RtpReceiverInterface>)nativeRtpReceiver
     NS_DESIGNATED_INITIALIZER;
 
++ (RTCRtpMediaType)mediaTypeForNativeMediaType:(cricket::MediaType)nativeMediaType;
+
 @end
 
 NS_ASSUME_NONNULL_END