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

webrtc/modules/remote_bitrate_estimator/test/estimators/congestion_window.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.
+ *
+ */
+
+#include "webrtc/modules/remote_bitrate_estimator/test/estimators/congestion_window.h"
+
+#include <algorithm>
+
+#include "webrtc/modules/remote_bitrate_estimator/test/estimators/bbr.h"
+
+namespace webrtc {
+namespace testing {
+namespace bwe {
+namespace {
+// kStartingCongestionWindow is used to set congestion window when bandwidth
+// delay product is equal to zero, so that we don't set window to zero as well.
+// Chosen randomly by me, because this value shouldn't make any significant
+// difference, as bandwidth delay product is more than zero almost every time.
+const int kStartingCongestionWindow = 6000;
+// Size of congestion window while in PROBE_RTT mode, suggested by BBR's source
+// code of QUIC's implementation.
+const int kMinimumCongestionWindow = 5840;
+}  // namespace
+
+CongestionWindow::CongestionWindow() : data_inflight_(0) {}
+
+CongestionWindow::~CongestionWindow() {}
+
+int CongestionWindow::GetCongestionWindow(BbrBweSender::Mode mode,
+                                          int64_t bandwidth_estimate,
+                                          int64_t min_rtt,
+                                          float gain) {
+  if (mode == BbrBweSender::PROBE_RTT)
+    return kMinimumCongestionWindow;
+  return GetTargetCongestionWindow(bandwidth_estimate, min_rtt, gain);
+}
+
+void CongestionWindow::PacketSent(size_t sent_packet_size) {
+  data_inflight_ += sent_packet_size;
+}
+
+void CongestionWindow::AckReceived(size_t received_packet_size) {
+  data_inflight_ -= received_packet_size;
+}
+
+int CongestionWindow::GetTargetCongestionWindow(int64_t bandwidth_estimate,
+                                                int64_t min_rtt,
+                                                float gain) {
+  int bdp = min_rtt * bandwidth_estimate;
+  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.
+  if (!congestion_window)
+    congestion_window = gain * kStartingCongestionWindow;
+  return std::max(congestion_window, kMinimumCongestionWindow);
+}
+}  // namespace bwe
+}  // namespace testing
+}  // namespace webrtc