relnote: Use event_time instead of ApproximateNow() in QUIC cubic code. Protected by --quic_use_eve…

net/quic/core/congestion_control/cubic.cc

 // 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.
 
 #include "net/quic/core/congestion_control/cubic.h"
 
 #include <algorithm>
 #include <cmath>
 #include <cstdint>
 
@@ skipping 88 matching lines @@
         static_cast<int>(kBetaLastMax * current_congestion_window);
   } else {
     last_max_congestion_window_ = current_congestion_window;
   }
   epoch_ = QuicTime::Zero();  // Reset time.
   return static_cast<int>(current_congestion_window * Beta());
 }
 
 QuicPacketCount Cubic::CongestionWindowAfterAck(
     QuicPacketCount current_congestion_window,
-    QuicTime::Delta delay_min) {
+    QuicTime::Delta delay_min,
+    QuicTime event_time) {
   acked_packets_count_ += 1;  // Packets acked.
   epoch_packets_count_ += 1;
-  QuicTime current_time = clock_->ApproximateNow();
+  QuicTime current_time = FLAGS_quic_use_event_time
+                              ? event_time
+                              : clock_->ApproximateNow();
 
   // Cubic is "independent" of RTT, the update is limited by the time elapsed.
   if (last_congestion_window_ == current_congestion_window &&
       (current_time - last_update_time_ <= MaxCubicTimeInterval())) {
     return std::max(last_target_congestion_window_,
                     estimated_tcp_congestion_window_);
   }
   last_congestion_window_ = current_congestion_window;
   last_update_time_ = current_time;
 
@@ skipping 71 matching lines @@
   // congestion_window, use highest (fastest).
   if (target_congestion_window < estimated_tcp_congestion_window_) {
     target_congestion_window = estimated_tcp_congestion_window_;
   }
 
   DVLOG(1) << "Final target congestion_window: " << target_congestion_window;
   return target_congestion_window;
 }
 
 }  // namespace net