Added implementation of three classes in BBR,with unit-tests.

webrtc/modules/remote_bitrate_estimator/test/estimators/min_rtt_filter.h

Index: webrtc/modules/remote_bitrate_estimator/test/estimators/min_rtt_filter.h
diff --git a/webrtc/modules/remote_bitrate_estimator/test/estimators/min_rtt_filter.h b/webrtc/modules/remote_bitrate_estimator/test/estimators/min_rtt_filter.h
index f41a4f0dad57ef9426094c4f51305649fa372e87..a6c649cba867b79257db77b80e386727d1786346 100644
--- a/webrtc/modules/remote_bitrate_estimator/test/estimators/min_rtt_filter.h
+++ b/webrtc/modules/remote_bitrate_estimator/test/estimators/min_rtt_filter.h
@@ -12,20 +12,37 @@
 #ifndef WEBRTC_MODULES_REMOTE_BITRATE_ESTIMATOR_TEST_ESTIMATORS_MIN_RTT_FILTER_H_
 #define WEBRTC_MODULES_REMOTE_BITRATE_ESTIMATOR_TEST_ESTIMATORS_MIN_RTT_FILTER_H_
 
+#include <cstdint>
+#include <limits>
+
+#include "webrtc/rtc_base/optional.h"
+
 namespace webrtc {
 namespace testing {
 namespace bwe {
 class MinRttFilter {
  public:
-  MinRttFilter();
-  ~MinRttFilter();
-  int64_t min_rtt();
-  void UpdateMinRtt(int64_t min_rtt);
+  MinRttFilter() {}
+  ~MinRttFilter() {}
+
+  rtc::Optional<int64_t> min_rtt() { return min_rtt_; }
+  void add_rtt_sample(int64_t rtt, int64_t now_ms) {
+    if (!min_rtt_ || rtt <= *min_rtt_) {
+      min_rtt_.emplace(rtt);
+      discovery_time_ms_ = now_ms;
+    }
+  }
+  int64_t discovery_time() { return discovery_time_ms_; }
 
   // Checks whether or not last discovered min_rtt value is older than x
-  // seconds.
-  bool MinRttExpired(int64_t now);
-  void set_min_rtt_discovery_time(int64_t discovery_time);
+  // milliseconds.
+  bool min_rtt_expired(int64_t now_ms, int64_t min_rtt_filter_window_size_ms) {
+    return now_ms - discovery_time_ms_ >= min_rtt_filter_window_size_ms;
+  }
+
+ private:
+  rtc::Optional<int64_t> min_rtt_;
+  int64_t discovery_time_ms_ = 0;
 };
 }  // namespace bwe
 }  // namespace testing