Refactor of QUIC's rtt storage and calculation to have a single RttStats

net/quic/congestion_control/fix_rate_sender.cc

Index: net/quic/congestion_control/fix_rate_sender.cc
diff --git a/net/quic/congestion_control/fix_rate_sender.cc b/net/quic/congestion_control/fix_rate_sender.cc
index fe10cdf2849233cb6a5a21ca2ec74077894bfc3d..c84828043e1ca3f3d517ac9ec2c2019dba410269 100644
--- a/net/quic/congestion_control/fix_rate_sender.cc
+++ b/net/quic/congestion_control/fix_rate_sender.cc
@@ -121,11 +121,6 @@ void FixRateSender::UpdateRtt(QuicTime::Delta rtt_sample) {
   latest_rtt_ = rtt_sample;
 }
 
-QuicTime::Delta FixRateSender::SmoothedRtt() const {
-  // TODO(satyamshekhar): Calculate and return smoothed rtt.
-  return latest_rtt_;
-}
-
 QuicTime::Delta FixRateSender::RetransmissionDelay() const {
   // TODO(pwestin): Calculate and return retransmission delay.
   // Use 2 * the latest RTT for now.