Update QuicSentPacketManager to sample a new recent min rtt within the

net/quic/quic_sent_packet_manager.cc

 // Copyright 2013 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/quic_sent_packet_manager.h"
 
 #include <algorithm>
 
 #include "base/logging.h"
 #include "base/stl_util.h"
@@ skipping 20 matching lines @@
 
 // Only exponentially back off the handshake timer 5 times due to a timeout.
 static const size_t kMaxHandshakeRetransmissionBackoffs = 5;
 static const size_t kMinHandshakeTimeoutMs = 10;
 
 // Sends up to two tail loss probes before firing an RTO,
 // per draft RFC draft-dukkipati-tcpm-tcp-loss-probe.
 static const size_t kDefaultMaxTailLossProbes = 2;
 static const int64 kMinTailLossProbeTimeoutMs = 10;
 
+// Number of samples before we force a new recent min rtt to be captured.
+static const size_t kNumMinRttSamplesAfterQuiescence = 2;
+
 bool HasCryptoHandshake(const TransmissionInfo& transmission_info) {
   if (transmission_info.retransmittable_frames == NULL) {
     return false;
   }
   return transmission_info.retransmittable_frames->HasCryptoHandshake() ==
       IS_HANDSHAKE;
 }
 
 }  // namespace
 
@@ skipping 386 matching lines @@
     TransmissionType transmission_type,
     HasRetransmittableData has_retransmittable_data) {
   DCHECK_LT(0u, sequence_number);
   LOG_IF(DFATAL, bytes == 0) << "Cannot send empty packets.";
   // In rare circumstances, the packet could be serialized, sent, and then acked
   // before OnPacketSent is called.
   if (!unacked_packets_.IsUnacked(sequence_number)) {
     return false;
   }
 
+  if (unacked_packets_.bytes_in_flight() == 0) {
+    // TODO(ianswett): Consider being less aggressive to force a new
+    // recent_min_rtt, likely by not discarding a relatively new sample.
+    DVLOG(1) << "Sampling a new recent min rtt within 2 samples. currently:"
+             << rtt_stats_.recent_min_rtt().ToMilliseconds() << "ms";
+    rtt_stats_.SampleNewRecentMinRtt(kNumMinRttSamplesAfterQuiescence);
+  }
+
   // Only track packets as pending that the send algorithm wants us to track.
   const bool pending =
       send_algorithm_->OnPacketSent(sent_time,
                                     unacked_packets_.bytes_in_flight(),
                                     sequence_number,
                                     bytes,
                                     has_retransmittable_data);
   unacked_packets_.SetSent(sequence_number, sent_time, bytes, pending);
 
   // Reset the retransmission timer anytime a pending packet is sent.
@@ skipping 306 matching lines @@
     return;
   }
 
   using_pacing_ = true;
   send_algorithm_.reset(
       new PacingSender(send_algorithm_.release(),
                        QuicTime::Delta::FromMicroseconds(1)));
 }
 
 }  // namespace net