Let FlexfecReceiveStreamImpl send RTCP RRs.

webrtc/modules/rtp_rtcp/source/flexfec_receiver.cc

Index: webrtc/modules/rtp_rtcp/source/flexfec_receiver.cc
diff --git a/webrtc/modules/rtp_rtcp/source/flexfec_receiver.cc b/webrtc/modules/rtp_rtcp/source/flexfec_receiver.cc
index 204ce84d2a56e5d01850f5994cb4c79c25c718d2..115f500d9c813eebff51c97035d5690cd7106532 100644
--- a/webrtc/modules/rtp_rtcp/source/flexfec_receiver.cc
+++ b/webrtc/modules/rtp_rtcp/source/flexfec_receiver.cc
@@ -45,7 +45,8 @@ FlexfecReceiver::FlexfecReceiver(
 
 FlexfecReceiver::~FlexfecReceiver() = default;
 
-bool FlexfecReceiver::AddAndProcessReceivedPacket(RtpPacketReceived packet) {
+bool FlexfecReceiver::AddAndProcessReceivedPacket(
+    const RtpPacketReceived& packet) {
   RTC_DCHECK_CALLED_SEQUENTIALLY(&sequence_checker_);
   if (!AddReceivedPacket(std::move(packet))) {
     return false;
@@ -58,7 +59,7 @@ FecPacketCounter FlexfecReceiver::GetPacketCounter() const {
   return packet_counter_;
 }
 
-bool FlexfecReceiver::AddReceivedPacket(RtpPacketReceived packet) {
+bool FlexfecReceiver::AddReceivedPacket(const RtpPacketReceived& packet) {
   RTC_DCHECK_CALLED_SEQUENTIALLY(&sequence_checker_);
 
   // RTP packets with a full base header (12 bytes), but without payload,