Add ability to handle data from multiple streams in RateAccCounter.

webrtc/video/stats_counter.h

Index: webrtc/video/stats_counter.h
diff --git a/webrtc/video/stats_counter.h b/webrtc/video/stats_counter.h
index c272b6278d0961b69362748ab7272ba5c4b2af71..cad5a63de74760f3f4f899a04402b38333d616e8 100644
--- a/webrtc/video/stats_counter.h
+++ b/webrtc/video/stats_counter.h
@@ -11,6 +11,8 @@
 #ifndef WEBRTC_VIDEO_STATS_COUNTER_H_
 #define WEBRTC_VIDEO_STATS_COUNTER_H_
 
+#include <limits>
+#include <map>
 #include <memory>
 
 #include "webrtc/base/constructormagic.h"
@@ -82,25 +84,34 @@ class StatsCounter {
 
   AggregatedStats GetStats();
 
+  // Holds gathered samples within a process interval.
+  struct Samples {
+    void Add(int sample);
+    void Set(int sample);
+    void Reset();
+
+    int max_ = std::numeric_limits<int>::min();
+    int64_t num_ = 0;
+    int64_t sum_ = 0;
+    int64_t last_sum_ = 0;
+  };
+
  protected:
   StatsCounter(Clock* clock,
                bool include_empty_intervals,
                StatsCounterObserver* observer);
 
   void Add(int sample);
-  void Set(int sample);
+  void Set(int sample, uint32_t ssrc);
 
-  int max_;
-  int64_t sum_;
-  int64_t num_samples_;
-  int64_t last_sum_;
+  const bool include_empty_intervals_;
+  std::map<uint32_t, Samples> samples_;  // Gathered samples mapped by SSRC.
 
  private:
   bool TimeToProcess();
   void TryProcess();
 
   Clock* const clock_;
-  const bool include_empty_intervals_;
   const std::unique_ptr<StatsCounterObserver> observer_;
   const std::unique_ptr<AggregatedCounter> aggregated_counter_;
   int64_t last_process_time_ms_;
@@ -218,7 +229,7 @@ class RateAccCounter : public StatsCounter {
                  bool include_empty_intervals);
   ~RateAccCounter() override {}
 
-  void Set(int sample);
+  void Set(int sample, uint32_t ssrc);
 
  private:
   bool GetMetric(int* metric) const override;