Fix bug where a connection switch causes BWE to be set to zero.

webrtc/modules/bitrate_controller/bitrate_controller_impl.cc

 /*
  *  Copyright (c) 2012 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 130 matching lines @@
                                       max_bitrate_bps);
   }
   MaybeTriggerOnNetworkChanged();
 }
 
 void BitrateControllerImpl::ResetBitrates(int bitrate_bps,
                                           int min_bitrate_bps,
                                           int max_bitrate_bps) {
   {
     rtc::CritScope cs(&critsect_);
+    if (bitrate_bps == -1) {

[terelius, 2016/07/05 13:55:36]

If -1 has a special meaning, isn't there a risk to introduce new bugs  if people
forget to handle that when making changes to the bitrate controller?

If we are changing the network, do we want to keep the bitrate estimate from the
old network, or reset it to the original default value?

[stefan-webrtc, 2016/07/07 11:50:46]

Good point, the correct behavior is to change to the original default value, I
think.

+      uint8_t loss;
+      int64_t rtt;
+      bandwidth_estimation_.CurrentEstimate(&bitrate_bps, &loss, &rtt);
+    }
     bandwidth_estimation_ = SendSideBandwidthEstimation(event_log_);
     bandwidth_estimation_.SetBitrates(bitrate_bps, min_bitrate_bps,
                                       max_bitrate_bps);
   }
   MaybeTriggerOnNetworkChanged();
 }
 
 void BitrateControllerImpl::SetReservedBitrate(uint32_t reserved_bitrate_bps) {
   {
     rtc::CritScope cs(&critsect_);
@@ skipping 97 matching lines @@
   bandwidth_estimation_.CurrentEstimate(&bitrate, &fraction_loss, &rtt);
   if (bitrate > 0) {
     bitrate = bitrate - std::min<int>(bitrate, reserved_bitrate_bps_);
     bitrate = std::max(bitrate, bandwidth_estimation_.GetMinBitrate());
     *bandwidth = bitrate;
     return true;
   }
   return false;
 }
 }  // namespace webrtc