Add FlexfecSender.

webrtc/modules/rtp_rtcp/source/ulpfec_generator.cc

Index: webrtc/modules/rtp_rtcp/source/ulpfec_generator.cc
diff --git a/webrtc/modules/rtp_rtcp/source/ulpfec_generator.cc b/webrtc/modules/rtp_rtcp/source/ulpfec_generator.cc
index 3c71c6383506c2870b8d9b73414ef8648ef8e2e5..c9de401d7103d15f1cd06454e7728bdbe12b0586 100644
--- a/webrtc/modules/rtp_rtcp/source/ulpfec_generator.cc
+++ b/webrtc/modules/rtp_rtcp/source/ulpfec_generator.cc
@@ -94,7 +94,10 @@ size_t RedPacket::length() const {
 }
 
 UlpfecGenerator::UlpfecGenerator()
-    : fec_(ForwardErrorCorrection::CreateUlpfec()),
+    : UlpfecGenerator(ForwardErrorCorrection::CreateUlpfec()) {}
+
+UlpfecGenerator::UlpfecGenerator(std::unique_ptr<ForwardErrorCorrection> fec)

[stefan-webrtc, 2016/11/02 13:02:42]

This is a bit weird. Why not have a single constructor and initialize like this:
fec_(ForwardErrorCorrection::CreateUlpfec())?

[brandtr, 2016/11/02 14:04:37]

Yes, it's a bit weird. With your suggestion however, the "normal user" of
UlpfecGenerator (i.e. RTPSenderVideo when it's sending RED+ULPFEC) will have to
be aware that UlpfecGenerator under the hood supports multiple FEC header
formatting routines. With this setup, the "normal user" will use the default
constructor, whereas the "friend user" (i.e., FlexfecSenderImpl) will use the
other constructor. (Note that the single-argument constructor is private.)

I don't see a need to make this a more general solution, where UlpfecGenerator
and FlexfecSenderImpl inherit from some common parent, for two reasons: 1) it's
our intention to completely change the interface of FlexfecSender when we move
it to PacedSender, and 2) eventually UlpfecGenerator will be deprecated.

[stefan-webrtc, 2016/11/03 13:42:40]

I see, you do need both constructors? I thought this second constructor was only
used from the first constructor, but if it's used elsewhere I understand.

+    : fec_(std::move(fec)),
       num_protected_frames_(0),
       min_num_media_packets_(1) {
   memset(&params_, 0, sizeof(params_));
@@ -140,7 +143,7 @@ int UlpfecGenerator::AddRtpPacketAndGenerateFec(const uint8_t* data_buffer,
   bool complete_frame = false;
   const bool marker_bit = (data_buffer[1] & kRtpMarkerBitMask) ? true : false;
   if (media_packets_.size() < kUlpfecMaxMediaPackets) {
-    // Generic FEC can only protect up to |kUlpfecMaxMediaPackets| packets.
+    // Our packet masks can only protect up to |kUlpfecMaxMediaPackets| packets.
     std::unique_ptr<ForwardErrorCorrection::Packet> packet(
         new ForwardErrorCorrection::Packet());
     packet->length = payload_length + rtp_header_length;