Reland of Add path for recovered packets from internal::Call to RtpStreamReceiver.

webrtc/modules/rtp_rtcp/include/flexfec_receiver.h

Index: webrtc/modules/rtp_rtcp/include/flexfec_receiver.h
diff --git a/webrtc/modules/rtp_rtcp/include/flexfec_receiver.h b/webrtc/modules/rtp_rtcp/include/flexfec_receiver.h
index f3894f5d7764170986a333d17e0d1d3520239b62..8f672fcc2dddff3c8d3dd8c761ad0d9f43166a63 100644
--- a/webrtc/modules/rtp_rtcp/include/flexfec_receiver.h
+++ b/webrtc/modules/rtp_rtcp/include/flexfec_receiver.h
@@ -18,7 +18,8 @@
 
 namespace webrtc {
 
-// Callback interface for packets recovered by FlexFEC.
+// Callback interface for packets recovered by FlexFEC. The implementation
+// should be able to demultiplex the recovered RTP packets based on SSRC.
 class RecoveredPacketReceiver {
  public:
   virtual bool OnRecoveredPacket(const uint8_t* packet, size_t length) = 0;