Use RateCounter for received bitrate stats.

webrtc/video/stats_counter_unittest.cc

Index: webrtc/video/stats_counter_unittest.cc
diff --git a/webrtc/video/stats_counter_unittest.cc b/webrtc/video/stats_counter_unittest.cc
index 5dd8b72cd6ebc2859bdc5221ca0fbdd73df788fa..d054eaa4b240cd720d09beaad690339a966a5bcc 100644
--- a/webrtc/video/stats_counter_unittest.cc
+++ b/webrtc/video/stats_counter_unittest.cc
@@ -72,6 +72,13 @@ TEST_F(StatsCounterTest, TestRegisterObserver) {
   EXPECT_EQ(1, observer->num_calls_);
 }
 
+TEST_F(StatsCounterTest, HasSample) {
+  AvgCounter counter(&clock_, nullptr);
+  EXPECT_FALSE(counter.HasSample());
+  counter.Add(1);
+  EXPECT_TRUE(counter.HasSample());
+}
+
 TEST_F(StatsCounterTest, VerifyProcessInterval) {
   StatsCounterObserverImpl* observer = new StatsCounterObserverImpl();
   AvgCounter counter(&clock_, observer);