Fix crash which happens when there's reordering in the beginning of a call.

webrtc/modules/remote_bitrate_estimator/remote_estimator_proxy.cc

Index: webrtc/modules/remote_bitrate_estimator/remote_estimator_proxy.cc
diff --git a/webrtc/modules/remote_bitrate_estimator/remote_estimator_proxy.cc b/webrtc/modules/remote_bitrate_estimator/remote_estimator_proxy.cc
index 524985c49077376454e17f61eb4feae8400e9d07..27a5dfc362d7ba9ddc1690e9e7ee151743f61d5e 100644
--- a/webrtc/modules/remote_bitrate_estimator/remote_estimator_proxy.cc
+++ b/webrtc/modules/remote_bitrate_estimator/remote_estimator_proxy.cc
@@ -89,7 +89,18 @@ void RemoteEstimatorProxy::Process() {
 
 void RemoteEstimatorProxy::OnPacketArrival(uint16_t sequence_number,
                                            int64_t arrival_time) {
+  // TODO(holmer): We should handle a backwards wrap here if the first
+  // sequence number was small and the new sequence number is large. The
+  // SequenceNumberUnwrapper doesn't do this, so we should replace this with
+  // calls to IsNewerSequenceNumber instead.
   int64_t seq = unwrapper_.Unwrap(sequence_number);
+  if (seq > window_start_seq_ + 0xFFFF / 2) {

[pbos-webrtc, 2016/07/18 08:53:57]

Should this check be using IsNewerSequenceNumber?

[stefan-webrtc, 2016/07/18 09:30:20]

That wouldn't be that simple to write I think. We want to capture if there was
reordering which also happened around a wrap, and if that happened when the
window_start_seq_ was <= 0xFFFF, as that would require seq to be negative. An
alternative would be to simply allow the unwrapper to return a negative seq (or
-1 because it failed), but then I'll have to go over more code to see that
nothing else breaks. If you prefer that I can certainly do that.

[pbos-webrtc, 2016/07/18 09:32:39]

Nah, no strong preferences if it doesn't make things simpler.

+    LOG(LS_WARNING) << "Skipping this sequence number (" << sequence_number
+                    << ") since it likely is reordered, but the unwrapper"
+                       "failed to handle it.Feedback window starts at "

[pbos-webrtc, 2016/07/18 08:53:57]

". F"

[stefan-webrtc, 2016/07/18 09:30:20]

Acknowledged.

+                    << window_start_seq_ << ".";
+    return;
+  }
 
   if (packet_arrival_times_.lower_bound(window_start_seq_) ==
       packet_arrival_times_.end()) {