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

webrtc/modules/remote_bitrate_estimator/test/estimators/congestion_window.cc

Index: webrtc/modules/remote_bitrate_estimator/test/estimators/congestion_window.cc
diff --git a/webrtc/modules/remote_bitrate_estimator/test/estimators/congestion_window.cc b/webrtc/modules/remote_bitrate_estimator/test/estimators/congestion_window.cc
index a52d17d7111e7d3d4084ab7bf4f61477140a7d5e..82d5b7b75b82465e93a163f123ab5db4f73d64f0 100644
--- a/webrtc/modules/remote_bitrate_estimator/test/estimators/congestion_window.cc
+++ b/webrtc/modules/remote_bitrate_estimator/test/estimators/congestion_window.cc
@@ -33,15 +33,13 @@ CongestionWindow::CongestionWindow() : data_inflight_bytes_(0) {}
 
 CongestionWindow::~CongestionWindow() {}
 
-int CongestionWindow::GetCongestionWindow(
-    BbrBweSender::Mode mode,
-    int64_t bandwidth_estimate_bytes_per_ms,
-    int64_t min_rtt_ms,
-    float gain) {
+int CongestionWindow::GetCongestionWindow(BbrBweSender::Mode mode,
+                                          int64_t bandwidth_estimate_bps,
+                                          rtc::Optional<int64_t> min_rtt_ms,
+                                          float gain) {
   if (mode == BbrBweSender::PROBE_RTT)
     return kMinimumCongestionWindow;
-  return GetTargetCongestionWindow(bandwidth_estimate_bytes_per_ms, min_rtt_ms,
-                                   gain);
+  return GetTargetCongestionWindow(bandwidth_estimate_bps, min_rtt_ms, gain);
 }
 
 void CongestionWindow::PacketSent(size_t sent_packet_size_bytes) {
@@ -53,10 +51,10 @@ void CongestionWindow::AckReceived(size_t received_packet_size_bytes) {
 }
 
 int CongestionWindow::GetTargetCongestionWindow(
-    int64_t bandwidth_estimate_bytes_per_ms,
-    int64_t min_rtt_ms,
+    int64_t bandwidth_estimate_bps,
+    rtc::Optional<int64_t> min_rtt_ms,
     float gain) {
-  int bdp = min_rtt_ms * bandwidth_estimate_bytes_per_ms;
+  int bdp = *min_rtt_ms * bandwidth_estimate_bps;
   int congestion_window = bdp * gain;
   // Congestion window could be zero in rare cases, when either no bandwidth
   // estimate is available, or path's min_rtt value is zero.