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

net/quic/congestion_control/rtt_stats.h

 // 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.
 //
 // A convenience class to store rtt samples and calculate smoothed rtt.
 
 #ifndef NET_QUIC_CONGESTION_CONTROL_RTT_STATS_H_
 #define NET_QUIC_CONGESTION_CONTROL_RTT_STATS_H_
 
 #include <algorithm>
@@ skipping 25 matching lines @@
   // is larger. The mean deviation is increased to the most recent deviation if
   // it's larger.
   void ExpireSmoothedMetrics();
 
   // Forces RttStats to sample a new recent min rtt within the next
   // |num_samples| UpdateRtt calls.
   void SampleNewRecentMinRtt(uint32 num_samples);
 
   QuicTime::Delta SmoothedRtt() const;
 
+  // Returns the min_rtt for the entire connection if a min has been measured.
+  // This returns an initial non-zero RTT estimate if no measurements have yet
+  // been made.
+  QuicTime::Delta MinRtt() const;
+
   int64 initial_rtt_us() const {
     return initial_rtt_us_;
   }
 
   // Sets an initial RTT to be used for SmoothedRtt before any RTT updates.
   void set_initial_rtt_us(int64 initial_rtt_us) {
     initial_rtt_us_ = initial_rtt_us;
   }
 
   QuicTime::Delta latest_rtt() const {
     return latest_rtt_;
   }
 
-  // Returns the min_rtt for the entire connection.
-  QuicTime::Delta min_rtt() const {
-    return min_rtt_;
-  }
-
   // Returns the min_rtt since SampleNewRecentMinRtt has been called, or the
   // min_rtt for the entire connection if SampleNewMinRtt was never called.
   QuicTime::Delta recent_min_rtt() const {
     return recent_min_rtt_.rtt;
   }
 
   QuicTime::Delta mean_deviation() const {
     return mean_deviation_;
   }
 
@@ skipping 34 matching lines @@
   RttSample recent_min_rtt_;  // a in the windowed algorithm.
   RttSample half_window_rtt_;  // b in the sampled algorithm.
   RttSample quarter_window_rtt_;  // c in the sampled algorithm.
 
   DISALLOW_COPY_AND_ASSIGN(RttStats);
 };
 
 }  // namespace net
 
 #endif  // NET_QUIC_CONGESTION_CONTROL_RTT_STATS_H_