Use LeastUnacked to calculate the packet number length instead of GetLeastPacketAwaitedByPeer.

net/quic/core/quic_connection.cc

Index: net/quic/core/quic_connection.cc
diff --git a/net/quic/core/quic_connection.cc b/net/quic/core/quic_connection.cc
index d35108cd6a2bf609fe18573405a1dd5e740b90a4..958b71233d696351d356972a345ac780deb6207d 100644
--- a/net/quic/core/quic_connection.cc
+++ b/net/quic/core/quic_connection.cc
@@ -1687,9 +1687,17 @@ bool QuicConnection::WritePacket(SerializedPacket* packet) {
     // TODO(ianswett): Change the packet number length and other packet creator
     // options by a more explicit API than setting a struct value directly,
     // perhaps via the NetworkChangeVisitor.
-    packet_generator_.UpdateSequenceNumberLength(
-        sent_packet_manager_->GetLeastPacketAwaitedByPeer(packet->path_id),
-        sent_packet_manager_->EstimateMaxPacketsInFlight(max_packet_length()));
+    if (FLAGS_quic_least_unacked_packet_number_length) {
+      packet_generator_.UpdateSequenceNumberLength(
+          sent_packet_manager_->GetLeastUnacked(packet->path_id),
+          sent_packet_manager_->EstimateMaxPacketsInFlight(
+              max_packet_length()));
+    } else {
+      packet_generator_.UpdateSequenceNumberLength(
+          sent_packet_manager_->GetLeastPacketAwaitedByPeer(packet->path_id),
+          sent_packet_manager_->EstimateMaxPacketsInFlight(
+              max_packet_length()));
+    }
   }
 
   bool reset_retransmission_alarm = sent_packet_manager_->OnPacketSent(
@@ -1703,9 +1711,17 @@ bool QuicConnection::WritePacket(SerializedPacket* packet) {
   if (FLAGS_quic_simple_packet_number_length) {
     // The packet number length must be updated after OnPacketSent, because it
     // may change the packet number length in packet.
-    packet_generator_.UpdateSequenceNumberLength(
-        sent_packet_manager_->GetLeastPacketAwaitedByPeer(packet->path_id),
-        sent_packet_manager_->EstimateMaxPacketsInFlight(max_packet_length()));
+    if (FLAGS_quic_least_unacked_packet_number_length) {
+      packet_generator_.UpdateSequenceNumberLength(
+          sent_packet_manager_->GetLeastUnacked(packet->path_id),
+          sent_packet_manager_->EstimateMaxPacketsInFlight(
+              max_packet_length()));
+    } else {
+      packet_generator_.UpdateSequenceNumberLength(
+          sent_packet_manager_->GetLeastPacketAwaitedByPeer(packet->path_id),
+          sent_packet_manager_->EstimateMaxPacketsInFlight(
+              max_packet_length()));
+    }
   }
 
   stats_.bytes_sent += result.bytes_written;