Reland of Only compare sequence numbers from the same SSRC in ForwardErrorCorrection.

webrtc/modules/rtp_rtcp/source/fec_test_helper.cc

Index: webrtc/modules/rtp_rtcp/source/fec_test_helper.cc
diff --git a/webrtc/modules/rtp_rtcp/source/fec_test_helper.cc b/webrtc/modules/rtp_rtcp/source/fec_test_helper.cc
index 74406db086b94deef2c94d67ce403af62dd9b7af..05655facac37a687ab158ab10073816d15a5adc8 100644
--- a/webrtc/modules/rtp_rtcp/source/fec_test_helper.cc
+++ b/webrtc/modules/rtp_rtcp/source/fec_test_helper.cc
@@ -78,7 +78,7 @@ ForwardErrorCorrection::PacketList MediaPacketGenerator::ConstructMediaPackets(
   RTC_DCHECK(media_packet);
   media_packet->data[1] |= 0x80;
 
-  fec_seq_num_ = seq_num;
+  next_seq_num_ = seq_num;
 
   return media_packets;
 }
@@ -88,8 +88,8 @@ ForwardErrorCorrection::PacketList MediaPacketGenerator::ConstructMediaPackets(
   return ConstructMediaPackets(num_media_packets, random_->Rand<uint16_t>());
 }
 
-uint16_t MediaPacketGenerator::GetFecSeqNum() {
-  return fec_seq_num_;
+uint16_t MediaPacketGenerator::GetNextSeqNum() {
+  return next_seq_num_;
 }
 
 AugmentedPacketGenerator::AugmentedPacketGenerator(uint32_t ssrc)