Fix crash when all acks in a feedback message arrive too late.

webrtc/modules/congestion_controller/delay_based_bwe.cc

 /*
  *  Copyright (c) 2016 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 154 matching lines @@
       last_logged_bitrate_(0),
       last_logged_state_(BandwidthUsage::kBwNormal) {
   LOG(LS_INFO) << "Using Trendline filter for delay change estimation.";
 
   network_thread_.DetachFromThread();
 }
 
 DelayBasedBwe::Result DelayBasedBwe::IncomingPacketFeedbackVector(
     const std::vector<PacketFeedback>& packet_feedback_vector) {
   RTC_DCHECK(network_thread_.CalledOnValidThread());
-  RTC_DCHECK(!packet_feedback_vector.empty());
 
   std::vector<PacketFeedback> sorted_packet_feedback_vector;
   SortPacketFeedbackVector(packet_feedback_vector,
                            &sorted_packet_feedback_vector);
+  // TOOD(holmer): An empty feedback vector here likely means that
+  // all acks were too late and that the send time history had
+  // timed out. We should reduce the rate when this occurs.
+  if (sorted_packet_feedback_vector.empty()) {
+    LOG(LS_WARNING) << "Very late feedback received.";
+    return DelayBasedBwe::Result();
+  }
 
   if (!uma_recorded_) {
     RTC_HISTOGRAM_ENUMERATION(kBweTypeHistogram,
                               BweNames::kSendSideTransportSeqNum,
                               BweNames::kBweNamesMax);
     uma_recorded_ = true;
   }
   Result aggregated_result;
   bool delayed_feedback = true;
   for (const auto& packet_feedback : sorted_packet_feedback_vector) {
@@ skipping 164 matching lines @@
 void DelayBasedBwe::SetMinBitrate(int min_bitrate_bps) {
   // Called from both the configuration thread and the network thread. Shouldn't
   // be called from the network thread in the future.
   rate_control_.SetMinBitrate(min_bitrate_bps);
 }
 
 int64_t DelayBasedBwe::GetProbingIntervalMs() const {
   return probing_interval_estimator_.GetIntervalMs();
 }
 }  // namespace webrtc