Fix a bug in QuicSentPacketManager::ClearPreviousRetransmissions where

net/quic/quic_sent_packet_manager_test.cc

Index: net/quic/quic_sent_packet_manager_test.cc
diff --git a/net/quic/quic_sent_packet_manager_test.cc b/net/quic/quic_sent_packet_manager_test.cc
index 8cd4f88fd611d40daa8f759526583d9394344ae9..4b576c615dafdf74c4e8b3870bb73ad5afa07918 100644
--- a/net/quic/quic_sent_packet_manager_test.cc
+++ b/net/quic/quic_sent_packet_manager_test.cc
@@ -388,6 +388,47 @@ TEST_F(QuicSentPacketManagerTest, TruncatedAck) {
   VerifyRetransmittablePackets(retransmittable, arraysize(retransmittable));
 }
 
+TEST_F(QuicSentPacketManagerTest, AckPreviousTransmissionThenTruncatedAck) {
+  SerializedPacket serialized_packet(CreateDataPacket(1));
+
+  manager_.OnSerializedPacket(serialized_packet);
+  RetransmitPacket(1, 2);
+  RetransmitPacket(2, 3);
+  RetransmitPacket(3, 4);
+  manager_.OnSerializedPacket(CreateDataPacket(5));
+  manager_.OnSerializedPacket(CreateDataPacket(6));
+  manager_.OnSerializedPacket(CreateDataPacket(7));
+  manager_.OnSerializedPacket(CreateDataPacket(8));
+  manager_.OnSerializedPacket(CreateDataPacket(9));
+
+  // Ack previous transmission
+  {
+    ReceivedPacketInfo received_info;
+    received_info.largest_observed = 2;
+    received_info.missing_packets.insert(1);
+    manager_.OnIncomingAck(received_info, QuicTime::Zero());
+    EXPECT_TRUE(manager_.IsUnacked(4));
+  }
+
+  // Truncated ack with 4 NACKs
+  {
+    ReceivedPacketInfo received_info;
+    received_info.largest_observed = 6;
+    received_info.missing_packets.insert(3);
+    received_info.missing_packets.insert(4);
+    received_info.missing_packets.insert(5);
+    received_info.missing_packets.insert(6);
+    received_info.is_truncated = true;
+    manager_.OnIncomingAck(received_info, QuicTime::Zero());
+  }
+
+  // High water mark will be raised.
+  QuicPacketSequenceNumber unacked[] = { 5, 6, 7, 8, 9 };
+  VerifyUnackedPackets(unacked, arraysize(unacked));
+  QuicPacketSequenceNumber retransmittable[] = { 5, 6, 7, 8, 9 };
+  VerifyRetransmittablePackets(retransmittable, arraysize(retransmittable));
+}
+
 TEST_F(QuicSentPacketManagerTest, SendDropAckRetransmitManyPackets) {
   manager_.OnSerializedPacket(CreateDataPacket(1));
   manager_.OnSerializedPacket(CreateDataPacket(2));