Update RTPSender::IsFecPacket for FlexFEC.

webrtc/modules/rtp_rtcp/source/rtp_sender.cc

Index: webrtc/modules/rtp_rtcp/source/rtp_sender.cc
diff --git a/webrtc/modules/rtp_rtcp/source/rtp_sender.cc b/webrtc/modules/rtp_rtcp/source/rtp_sender.cc
index 269e4056fdba66b075ffc32b90e42eee2f534c9a..a63ace51be080d7294e07671108842e2242af887 100644
--- a/webrtc/modules/rtp_rtcp/source/rtp_sender.cc
+++ b/webrtc/modules/rtp_rtcp/source/rtp_sender.cc
@@ -807,14 +807,18 @@ void RTPSender::UpdateRtpStats(const RtpPacketToSend& packet,
 }
 
 bool RTPSender::IsFecPacket(const RtpPacketToSend& packet) const {
-  if (!video_) {
+  if (!video_)
     return false;
-  }
+
+  // FlexFEC.
+  if (packet.Ssrc() == FlexfecSsrc())
+    return true;
+
+  // RED+ULPFEC.
   int pt_red;
   int pt_fec;
   video_->GetUlpfecConfig(&pt_red, &pt_fec);
-  const bool fec_enabled = (pt_fec != -1);

[brandtr, 2016/11/14 08:01:34]

This was weird. If for some reason a FEC packet was sent to this function, when
FEC was disabled, it would not be counted as a FEC packet. Even though it was a
FEC packet...?

[danilchap, 2016/11/14 10:23:39]

look like leftover from older refactorings, agree not needed now since
static_cast<int>(uint8_t) can't be -1.

it is not obvious what would happen if for some reason payload() will return
signed char* instead,
Still shouldn't be needed since pt_fec can't be more that 127 (DCHECKed when it
is set)

-  return fec_enabled && static_cast<int>(packet.PayloadType()) == pt_red &&
+  return static_cast<int>(packet.PayloadType()) == pt_red &&
          static_cast<int>(packet.payload()[0]) == pt_fec;
 }