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

webrtc/modules/bitrate_controller/bitrate_controller_impl.cc

Index: webrtc/modules/bitrate_controller/bitrate_controller_impl.cc
diff --git a/webrtc/modules/bitrate_controller/bitrate_controller_impl.cc b/webrtc/modules/bitrate_controller/bitrate_controller_impl.cc
index 8a2464d09c3d5124c8585f6b4996ba141ed12ffd..6ec1f12c30fdbe3700745c45cfdc8bee86753308 100644
--- a/webrtc/modules/bitrate_controller/bitrate_controller_impl.cc
+++ b/webrtc/modules/bitrate_controller/bitrate_controller_impl.cc
@@ -148,6 +148,11 @@ void BitrateControllerImpl::ResetBitrates(int 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);