Populate FasterExtraStats for QUIC requests

net/quic/congestion_control/send_algorithm_interface.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // The pure virtual class for send side congestion control algorithm.
 
 #ifndef NET_QUIC_CONGESTION_CONTROL_SEND_ALGORITHM_INTERFACE_H_
 #define NET_QUIC_CONGESTION_CONTROL_SEND_ALGORITHM_INTERFACE_H_
 
 #include <algorithm>
@@ skipping 74 matching lines @@
 
   // Get the send algorithm specific retransmission delay, called RTO in TCP,
   // Note 1: the caller is responsible for sanity checking this value.
   // Note 2: this will return zero if we don't have enough data for an estimate.
   virtual QuicTime::Delta RetransmissionDelay() const = 0;
 
   // Returns the size of the current congestion window in bytes.  Note, this is
   // not the *available* window.  Some send algorithms may not use a congestion
   // window and will return 0.
   virtual QuicByteCount GetCongestionWindow() const = 0;
+
+  // Returns the size of the slow start congestion window in bytes,
+  // aka ssthresh.  Some send algorithms do not define a slow start
+  // threshold and will return 0.
+  virtual QuicByteCount GetSlowStartThreshold() const = 0;
 };
 
 }  // namespace net
 
 #endif  // NET_QUIC_CONGESTION_CONTROL_SEND_ALGORITHM_INTERFACE_H_