relnote: Add a new LazyFack loss detection to QUIC triggered by the LFAK connection option.

net/quic/core/congestion_control/general_loss_algorithm_test.cc

Index: net/quic/core/congestion_control/general_loss_algorithm_test.cc
diff --git a/net/quic/core/congestion_control/general_loss_algorithm_test.cc b/net/quic/core/congestion_control/general_loss_algorithm_test.cc
index 107674dbdadf8f6ddefac3720d14e8bf64d5096f..0a0725ef82e16f9a04fdfb3626823f6186100d3f 100644
--- a/net/quic/core/congestion_control/general_loss_algorithm_test.cc
+++ b/net/quic/core/congestion_control/general_loss_algorithm_test.cc
@@ -232,6 +232,73 @@ TEST_F(GeneralLossAlgorithmTest, AlwaysLosePacketSent1RTTEarlier) {
   VerifyLosses(2, lost, arraysize(lost));
 }
 
+// NoFack loss detection tests.
+TEST_F(GeneralLossAlgorithmTest, LazyFackNackRetransmit1Packet) {
+  loss_algorithm_.SetLossDetectionType(kLazyFack);
+  const size_t kNumSentPackets = 5;
+  // Transmit 5 packets.
+  for (size_t i = 1; i <= kNumSentPackets; ++i) {
+    SendDataPacket(i);
+  }
+  // No loss on one ack.
+  unacked_packets_.RemoveFromInFlight(2);
+  VerifyLosses(2, nullptr, 0);
+  // No loss on two acks.
+  unacked_packets_.RemoveFromInFlight(3);
+  VerifyLosses(3, nullptr, 0);
+  // Loss on three acks.
+  unacked_packets_.RemoveFromInFlight(4);
+  QuicPacketNumber lost[] = {1};
+  VerifyLosses(4, lost, arraysize(lost));
+  EXPECT_EQ(QuicTime::Zero(), loss_algorithm_.GetLossTimeout());
+}
+
+// A stretch ack is an ack that covers more than 1 packet of previously
+// unacknowledged data.
+TEST_F(GeneralLossAlgorithmTest,
+       LazyFackNoNackRetransmit1PacketWith1StretchAck) {
+  loss_algorithm_.SetLossDetectionType(kLazyFack);
+  const size_t kNumSentPackets = 10;
+  // Transmit 10 packets.
+  for (size_t i = 1; i <= kNumSentPackets; ++i) {
+    SendDataPacket(i);
+  }
+
+  // Nack the first packet 3 times in a single StretchAck.
+  unacked_packets_.RemoveFromInFlight(2);
+  unacked_packets_.RemoveFromInFlight(3);
+  unacked_packets_.RemoveFromInFlight(4);
+  VerifyLosses(4, nullptr, 0);
+  // The timer isn't set because we expect more acks.
+  EXPECT_EQ(QuicTime::Zero(), loss_algorithm_.GetLossTimeout());
+  // Process another ack and then packet 1 will be lost.
+  unacked_packets_.RemoveFromInFlight(5);
+  QuicPacketNumber lost[] = {1};
+  VerifyLosses(5, lost, arraysize(lost));
+  EXPECT_EQ(QuicTime::Zero(), loss_algorithm_.GetLossTimeout());
+}
+
+// Ack a packet 3 packets ahead does not cause a retransmit.
+TEST_F(GeneralLossAlgorithmTest, LazyFackNackRetransmit1PacketSingleAck) {
+  loss_algorithm_.SetLossDetectionType(kLazyFack);
+  const size_t kNumSentPackets = 10;
+  // Transmit 10 packets.
+  for (size_t i = 1; i <= kNumSentPackets; ++i) {
+    SendDataPacket(i);
+  }
+
+  // Nack the first packet 3 times in an AckFrame with three missing packets.
+  unacked_packets_.RemoveFromInFlight(4);
+  VerifyLosses(4, nullptr, 0);
+  // The timer isn't set because we expect more acks.
+  EXPECT_EQ(QuicTime::Zero(), loss_algorithm_.GetLossTimeout());
+  // Process another ack and then packet 1 and 2 will be lost.
+  unacked_packets_.RemoveFromInFlight(5);
+  QuicPacketNumber lost[] = {1, 2};
+  VerifyLosses(5, lost, arraysize(lost));
+  EXPECT_EQ(QuicTime::Zero(), loss_algorithm_.GetLossTimeout());
+}
+
 // Time-based loss detection tests.
 TEST_F(GeneralLossAlgorithmTest, NoLossFor500Nacks) {
   loss_algorithm_.SetLossDetectionType(kTime);