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

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

 /*
  *  Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 28 matching lines @@
   congestion_window.PacketSent(10);
   congestion_window.PacketSent(9);
   EXPECT_EQ(congestion_window.data_inflight(), 20u);
   congestion_window.AckReceived(20);
   EXPECT_EQ(congestion_window.data_inflight(), 0u);
 }
 
 TEST(CongestionWindowTest, ZeroBandwidthDelayProduct) {
   CongestionWindow congestion_window;
   int64_t target_congestion_window =
-      congestion_window.GetTargetCongestionWindow(100, 0, 2.885f);
+      congestion_window.GetTargetCongestionWindow(
+          100, rtc::Optional<int64_t>(0), 2.885f);
   EXPECT_EQ(target_congestion_window, 2.885f * kStartingCongestionWindow);
 }
 
 TEST(CongestionWindowTest, BelowMinimumTargetCongestionWindow) {
   CongestionWindow congestion_window;
   int64_t target_congestion_window =
-      congestion_window.GetTargetCongestionWindow(100, 2, 2.885f);
+      congestion_window.GetTargetCongestionWindow(
+          100, rtc::Optional<int64_t>(2), 2.885f);
   EXPECT_EQ(target_congestion_window, kMinimumCongestionWindow);
 }
 
 TEST(CongestionWindowTest, AboveMinimumTargetCongestionWindow) {
   CongestionWindow congestion_window;
   int64_t target_congestion_window =
-      congestion_window.GetTargetCongestionWindow(100000, 2, 2.885f);
+      congestion_window.GetTargetCongestionWindow(
+          100000, rtc::Optional<int64_t>(2), 2.885f);
   EXPECT_EQ(target_congestion_window, 577000);
 }
 
 TEST(CongestionWindowTest, MinimumCongestionWindow) {
   CongestionWindow congestion_window;
-  int64_t cwnd = congestion_window.GetCongestionWindow(BbrBweSender::PROBE_RTT,
-                                                       100, 100, 2.885f);
+  int64_t cwnd = congestion_window.GetCongestionWindow(
+      BbrBweSender::PROBE_RTT, 100, rtc::Optional<int64_t>(100), 2.885f);
   EXPECT_EQ(cwnd, kMinimumCongestionWindow);
 }
 
 TEST(CongestionWindowTest, CalculateCongestionWindow) {
   CongestionWindow congestion_window;
-  int64_t cwnd = congestion_window.GetCongestionWindow(BbrBweSender::STARTUP,
-                                                       100, 100, 2.885f);
+  int64_t cwnd = congestion_window.GetCongestionWindow(
+      BbrBweSender::STARTUP, 100, rtc::Optional<int64_t>(100l), 2.885f);
   EXPECT_EQ(cwnd, 28850);
 }
 }  // namespace bwe
 }  // namespace testing
 }  // namespace webrtc