Reset QUIC's retransmission counters whenever a new packet is acked

net/quic/quic_sent_packet_manager.cc

Index: net/quic/quic_sent_packet_manager.cc
diff --git a/net/quic/quic_sent_packet_manager.cc b/net/quic/quic_sent_packet_manager.cc
index af9a507a59c00a3ffd3328f7253be710173ecd7f..a25cb5e6c9f4a16c07ad0666f4541ef7652d6ef7 100644
--- a/net/quic/quic_sent_packet_manager.cc
+++ b/net/quic/quic_sent_packet_manager.cc
@@ -181,19 +181,17 @@ void QuicSentPacketManager::OnRetransmittedPacket(
 
 bool QuicSentPacketManager::OnIncomingAck(
     const ReceivedPacketInfo& received_info, QuicTime ack_receive_time) {
-  // Determine if the least unacked sequence number is being acked.
-  QuicPacketSequenceNumber least_unacked_sent_before =
-      GetLeastUnackedSentPacket();
-  // TODO(ianswett): Consider a non-TCP metric for determining the connection
-  // is making progress, since QUIC has out of order delivery.
-  bool new_least_unacked = !IsAwaitingPacket(received_info,
-                                             least_unacked_sent_before);
-
+  // We rely on delta_time_largest_observed to compute an RTT estimate, so
+  // we only update rtt when the largest observed gets acked.
+  bool largest_observed_acked =
+      ContainsKey(unacked_packets_, received_info.largest_observed);
   MaybeUpdateRTT(received_info, ack_receive_time);
   HandleAckForSentPackets(received_info);
   MaybeRetransmitOnAckFrame(received_info, ack_receive_time);
 
-  if (new_least_unacked) {
+  // Anytime we are making forward progress and have a new RTT estimate, reset
+  // the backoff counters.
+  if (largest_observed_acked) {
     // Reset all retransmit counters any time a new packet is acked.
     consecutive_rto_count_ = 0;
     consecutive_tlp_count_ = 0;