Update from https://crrev.com/316786

net/quic/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/congestion_control/cubic.h"
 
 #include <algorithm>
 #include <cmath>
 
 #include "base/basictypes.h"
 #include "base/logging.h"
 #include "base/time/time.h"
-#include "net/quic/congestion_control/cube_root.h"
 #include "net/quic/quic_flags.h"
 #include "net/quic/quic_protocol.h"
 
 using std::max;
 
 namespace net {
 
 namespace {
 
 // Constants based on TCP defaults.
@@ skipping 105 matching lines @@
     // First ACK after a loss event.
     DVLOG(1) << "Start of epoch";
     epoch_ = current_time;  // Start of epoch.
     acked_packets_count_ = 1;  // Reset count.
     // Reset estimated_tcp_congestion_window_ to be in sync with cubic.
     estimated_tcp_congestion_window_ = current_congestion_window;
     if (last_max_congestion_window_ <= current_congestion_window) {
       time_to_origin_point_ = 0;
       origin_point_congestion_window_ = current_congestion_window;
     } else {
-      if (FLAGS_quic_use_std_cbrt) {
-        time_to_origin_point_ = static_cast<uint32>(
-            cbrt(kCubeFactor *
-                 (last_max_congestion_window_ - current_congestion_window)));
-      } else {
-        // TODO(rjshade): Remove CubeRoot source when removing
-        // FLAGS_quic_use_std_cbrt.
-        time_to_origin_point_ =
-            CubeRoot::Root(kCubeFactor * (last_max_congestion_window_ -
-                                          current_congestion_window));
-      }
+      time_to_origin_point_ =
+          static_cast<uint32>(cbrt(kCubeFactor * (last_max_congestion_window_ -
+                                                  current_congestion_window)));
       origin_point_congestion_window_ =
           last_max_congestion_window_;
     }
   }
   // Change the time unit from microseconds to 2^10 fractions per second. Take
   // the round trip time in account. This is done to allow us to use shift as a
   // divide operator.
   int64 elapsed_time =
       (current_time.Add(delay_min).Subtract(epoch_).ToMicroseconds() << 10) /
       base::Time::kMicrosecondsPerSecond;
@@ skipping 31 matching lines @@
   // congestion_window, use highest (fastest).
   if (target_congestion_window < estimated_tcp_congestion_window_) {
     target_congestion_window = estimated_tcp_congestion_window_;
   }
 
   DVLOG(1) << "Target congestion_window: " << target_congestion_window;
   return target_congestion_window;
 }
 
 }  // namespace net