Reverse |rtx_payload_types| map, and rename.

webrtc/video/video_receive_stream.cc

Index: webrtc/video/video_receive_stream.cc
diff --git a/webrtc/video/video_receive_stream.cc b/webrtc/video/video_receive_stream.cc
index 50b3321ee1ae4a1f8e22d4bec808bd43202324f2..8434e970c450f6b7b560fc750d52e81984b81912 100644
--- a/webrtc/video/video_receive_stream.cc
+++ b/webrtc/video/video_receive_stream.cc
@@ -94,8 +94,8 @@ std::string VideoReceiveStream::Config::Rtp::ToString() const {
   ss << ", ulpfec: " << ulpfec.ToString();
   ss << ", rtx_ssrc: " << rtx_ssrc;
   ss << ", rtx_payload_types: {";
-  for (auto& kv : rtx_payload_types) {
-    ss << kv.first << " (apt) -> " << kv.second << " (pt), ";
+  for (auto& kv : media_pt_by_rtx_pt) {
+    ss << kv.first << " (pt) -> " << kv.second << " (apt), ";
   }
   ss << '}';
   ss << ", extensions: [";