Round results of multiplying QuicBandwidth and QuicTime::Delta rather than truncating. No behavior…

net/quic/core/congestion_control/rtt_stats_test.cc

Index: net/quic/core/congestion_control/rtt_stats_test.cc
diff --git a/net/quic/core/congestion_control/rtt_stats_test.cc b/net/quic/core/congestion_control/rtt_stats_test.cc
index 6848e9b8f31b2f4b8c2b0629272a9e34c52ce516..d894bebd0bedf1d79f900e8dc6a64ac51504e3c2 100644
--- a/net/quic/core/congestion_control/rtt_stats_test.cc
+++ b/net/quic/core/congestion_control/rtt_stats_test.cc
@@ -4,6 +4,7 @@
 
 #include "net/quic/core/congestion_control/rtt_stats.h"
 
+#include <cmath>
 #include <vector>
 
 #include "base/logging.h"
@@ -53,6 +54,20 @@ TEST_F(RttStatsTest, SmoothedRtt) {
   EXPECT_EQ(QuicTime::Delta::FromMilliseconds(200), rtt_stats_.smoothed_rtt());
 }
 
+// Ensure that the potential rounding artifacts in EWMA calculation do not cause
+// the SRTT to drift too far from the exact value.
+TEST_F(RttStatsTest, SmoothedRttStability) {
+  for (size_t time = 3; time < 20000; time++) {
+    RttStats stats;
+    for (size_t i = 0; i < 100; i++) {
+      stats.UpdateRtt(QuicTime::Delta::FromMicroseconds(time),
+                      QuicTime::Delta::FromMilliseconds(0), QuicTime::Zero());
+      int64_t time_delta_us = stats.smoothed_rtt().ToMicroseconds() - time;
+      ASSERT_LE(std::abs(time_delta_us), 1);
+    }
+  }
+}
+
 TEST_F(RttStatsTest, PreviousSmoothedRtt) {
   // Verify that ack_delay is corrected for in Smoothed RTT.
   rtt_stats_.UpdateRtt(QuicTime::Delta::FromMilliseconds(300),