Add a QuicSustainedBandwidthEstimator class. Not yet used.

net/quic/quic_sustained_bandwidth_recorder.cc

+// Copyright (c) 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "net/quic/quic_sustained_bandwidth_recorder.h"
+
+#include "base/logging.h"
+#include "net/quic/quic_bandwidth.h"
+#include "net/quic/quic_time.h"
+
+namespace net {
+
+QuicSustainedBandwidthRecorder::QuicSustainedBandwidthRecorder()
+    : has_estimate_(false),
+      is_recording_(false),
+      bandwidth_estimate_(QuicBandwidth::Zero()),
+      max_bandwidth_estimate_(QuicBandwidth::Zero()),
+      max_bandwidth_timestamp_(0),
+      start_time_(QuicTime::Zero()) {}
+
+void QuicSustainedBandwidthRecorder::RecordEstimate(bool is_reliable_estimate,
+                                                    QuicBandwidth bandwidth,
+                                                    QuicTime estimate_time,
+                                                    QuicWallTime wall_time,
+                                                    QuicTime::Delta srtt) {
+  if (!is_reliable_estimate) {
+    is_recording_ = false;
+    DVLOG(1) << "Stopped recording due to unreliable estimate at: "
+             << estimate_time.ToDebuggingValue();
+    return;
+  }
+
+  if (!is_recording_) {
+    // This is the first estimate of a new recording period.
+    start_time_ = estimate_time;
+    is_recording_ = true;
+    DVLOG(1) << "Started recording at: " << start_time_.ToDebuggingValue();
+    return;
+  }
+
+  // If we have been recording for at least 3 * srtt, then record the latest
+  // bandwidth estimate as a valid sustained bandwidth estimate.
+  if (estimate_time.Subtract(start_time_) >= srtt.Multiply(3)) {
+    has_estimate_ = true;
+    bandwidth_estimate_ = bandwidth;
+    DVLOG(1) << "New sustained bandwidth estimate (KBytes/s): "
+             << bandwidth_estimate_.ToKBytesPerSecond();
+  }
+
+  // Check for an increase in max bandwidth.
+  if (bandwidth > max_bandwidth_estimate_) {
+    max_bandwidth_estimate_ = bandwidth;
+    max_bandwidth_timestamp_ = wall_time.ToUNIXSeconds();
+    DVLOG(1) << "New max bandwidth estimate (KBytes/s): "
+             << max_bandwidth_estimate_.ToKBytesPerSecond();
+  }
+}
+
+}  // namespace net