Support multiple rtx codecs.

webrtc/video/video_send_stream.cc

Index: webrtc/video/video_send_stream.cc
diff --git a/webrtc/video/video_send_stream.cc b/webrtc/video/video_send_stream.cc
index 656d5517941754df85a99a073d9634718a46c365..08dcd77ac69c749ac609e63c73d1f65c0490b5bb 100644
--- a/webrtc/video/video_send_stream.cc
+++ b/webrtc/video/video_send_stream.cc
@@ -494,6 +494,11 @@ void VideoSendStream::ConfigureSsrcs() {
   RTC_DCHECK_GE(config_.rtp.rtx.payload_type, 0);
   vie_channel_->SetRtxSendPayloadType(config_.rtp.rtx.payload_type,
                                       config_.encoder_settings.payload_type);
+  if (config_.rtp.fec.red_payload_type != -1 &&
+      config_.rtp.fec.red_rtx_payload_type != -1) {
+    vie_channel_->SetRtxSendPayloadType(config_.rtp.fec.red_rtx_payload_type,
+                                        config_.rtp.fec.red_payload_type);
+  }
 }
 
 std::map<uint32_t, RtpState> VideoSendStream::GetRtpStates() const {