Fixes two div by zero bugs in QUIC's BBR pacing code that caused server

net/quic/congestion_control/rtt_stats.cc

 // Copyright 2014 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/rtt_stats.h"
 
 #include <complex>  // std::abs
 
 using std::max;
 
@@ skipping 46 matching lines @@
   if (send_delta > ack_delay) {
     rtt_sample = send_delta.Subtract(ack_delay);
   } else if (!HasUpdates()) {
     // Even though we received information from the peer suggesting
     // an invalid (negative) RTT, we can use the send delta as an
     // approximation until we get a better estimate.
     rtt_sample = send_delta;
   }
 
   if (rtt_sample.IsInfinite() || rtt_sample.IsZero()) {
-    DVLOG(1) << "Ignoring rtt, because it's "
-             << (rtt_sample.IsZero() ? "Zero" : "Infinite");
+    LOG(WARNING) << "Ignoring rtt, because it's "
+                 << (rtt_sample.IsZero() ? "Zero" : "Infinite");
     return;
   }
-  // RTT can't be negative.
+  // RTT can't be non-positive.
   DCHECK_LT(0, rtt_sample.ToMicroseconds());
 
   latest_rtt_ = rtt_sample;
   // First time call or link delay decreases.
   if (min_rtt_.IsZero() || min_rtt_ > rtt_sample) {
     min_rtt_ = rtt_sample;
   }
   UpdateRecentMinRtt(rtt_sample, now);
   // First time call.
   if (!HasUpdates()) {
@@ skipping 49 matching lines @@
   }
 }
 
 QuicTime::Delta RttStats::SmoothedRtt() const {
   if (!HasUpdates()) {
     return QuicTime::Delta::FromMicroseconds(initial_rtt_us_);
   }
   return smoothed_rtt_;
 }
 
+QuicTime::Delta RttStats::MinRtt() const {
+  if (!HasUpdates()) {
+    return QuicTime::Delta::FromMicroseconds(initial_rtt_us_);
+  }
+  return min_rtt_;
+}
+
 }  // namespace net