Add TransportFeedbackPacketLossTracker.

webrtc/modules/rtp_rtcp/source/rtcp_packet/transport_feedback.h

Index: webrtc/modules/rtp_rtcp/source/rtcp_packet/transport_feedback.h
diff --git a/webrtc/modules/rtp_rtcp/source/rtcp_packet/transport_feedback.h b/webrtc/modules/rtp_rtcp/source/rtcp_packet/transport_feedback.h
index 03a1c4f728ac217d4cce1c0d03add9cb1bef7eb7..8f743c68c231c0c0cc338d96ed6d473643451152 100644
--- a/webrtc/modules/rtp_rtcp/source/rtcp_packet/transport_feedback.h
+++ b/webrtc/modules/rtp_rtcp/source/rtcp_packet/transport_feedback.h
@@ -46,8 +46,8 @@ class TransportFeedback : public Rtpfb {
     kReceivedLargeDelta,
   };
 
-  uint16_t GetBaseSequence() const;
-  std::vector<TransportFeedback::StatusSymbol> GetStatusVector() const;
+  virtual uint16_t GetBaseSequence() const;
+  virtual std::vector<TransportFeedback::StatusSymbol> GetStatusVector() const;

[kwiberg-webrtc, 2016/12/22 02:31:41]

I realize this is the quickest way to let you customize these two methods while
keeping the rest of this class's behavior, but I'm really not a fan of state in
base classes or using virtual methods for anything but interfaces. I'm lazy, and
dislike having to work hard to read code...

If I were you, I'd consider something like defining an interface for the
behavior of these two methods, and letting the TransportFeedback constructor
take an argument of this type. (It would probably be even better to turn
TransportFeedback and/or Rtpfb into interfaces and have normal and fuzzer
implementations of them, but this may be a lot more work than you want.) But
don't do this if you don't think it'd be an improvement.

[minyue-webrtc, 2016/12/28 14:48:32]

I would really like to have a TransportFeedback interface. I was lazy and did
not want to make a big change. But I think it should be a good thing to do and
so I tried. See the new patch set.

   std::vector<int16_t> GetReceiveDeltas() const;
 
   // Get the reference time in microseconds, including any precision loss.