Use RateCounter for received bitrate stats.

webrtc/video/stats_counter.h

 /*
  *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 64 matching lines @@
 // Note: StatsCounter takes ownership of |observer|.
 
 class StatsCounter {
  public:
   virtual ~StatsCounter();
 
   virtual bool GetMetric(int* metric) const = 0;
 
   AggregatedStats GetStats();
 
+  // Checks if a sample has been added (i.e. Add or Set called).
+  bool HasSample() const;
+
  protected:
   StatsCounter(Clock* clock,
                bool include_empty_intervals,
                StatsCounterObserver* observer);
 
   void Add(int sample);
   void Set(int sample);
 
   int max_;
   int64_t sum_;
@@ skipping 127 matching lines @@
 
  private:
   bool GetMetric(int* metric) const override;
 
   RTC_DISALLOW_COPY_AND_ASSIGN(RateAccCounter);
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_VIDEO_STATS_COUNTER_H_