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

webrtc/modules/rtp_rtcp/source/fec_test_helper.cc

 /*
  *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 60 matching lines @@
     for (size_t j = 12; j < media_packet->length; ++j)
       media_packet->data[j] = random_->Rand<uint8_t>();
     seq_num++;
     media_packets.push_back(std::move(media_packet));
   }
   // Last packet, set marker bit.
   ForwardErrorCorrection::Packet* media_packet = media_packets.back().get();
   RTC_DCHECK(media_packet);
   media_packet->data[1] |= 0x80;
 
-  fec_seq_num_ = seq_num;
+  next_seq_num_ = seq_num;
 
   return media_packets;
 }
 
 ForwardErrorCorrection::PacketList MediaPacketGenerator::ConstructMediaPackets(
     int num_media_packets) {
   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)
     : num_packets_(0), ssrc_(ssrc), seq_num_(0), timestamp_(0) {}
 
 void AugmentedPacketGenerator::NewFrame(size_t num_packets) {
   num_packets_ = num_packets;
   timestamp_ += kPacketTimestampIncrement;
 }
 
@@ skipping 105 matching lines @@
   red_packet->data[1] &= 0x80;             // Reset.
   red_packet->data[1] += kRedPayloadType;  // Replace.
 
   // Add RED header, f-bit always 0.
   red_packet->data[header_length] = payload_type;
 }
 
 }  // namespace fec
 }  // namespace test
 }  // namespace webrtc