Fix a bug where the packet was put into unacked packets when it was

net/quic/quic_connection.cc

Index: net/quic/quic_connection.cc
diff --git a/net/quic/quic_connection.cc b/net/quic/quic_connection.cc
index 51991be46cd61a0f983c3b15e80945075e657d8f..497aa929e30c06fe54cfab1ae7825b9b7650c8b6 100644
--- a/net/quic/quic_connection.cc
+++ b/net/quic/quic_connection.cc
@@ -1196,19 +1196,15 @@ bool QuicConnection::ShouldDiscardPacket(
     return true;
   }
 
-  if (retransmittable == HAS_RETRANSMITTABLE_DATA) {
-    if (!sent_packet_manager_.IsUnacked(sequence_number)) {
-      // This is a crazy edge case, but if we retransmit a packet,
-      // (but have to queue it for some reason) then receive an ack
-      // for the previous transmission (but not the retransmission)
-      // then receive a truncated ACK which causes us to raise the
-      // high water mark, all before we're able to send the packet
-      // then we can simply drop it.
-      DVLOG(1) << ENDPOINT << "Dropping packet: " << sequence_number
-                 << " since it has already been acked.";
-      return true;
-    }
+  // If the packet has been discarded before sending, don't send it.
+  // This occurs if a packet gets serialized, queued, then discarded.
+  if (!sent_packet_manager_.IsUnacked(sequence_number)) {
+    DVLOG(1) << ENDPOINT << "Dropping packet before sending: "
+             << sequence_number << " since it has already been discarded.";
+    return true;
+  }
 
+  if (retransmittable == HAS_RETRANSMITTABLE_DATA) {
     if (sent_packet_manager_.IsPreviousTransmission(sequence_number)) {
       // If somehow we have already retransmitted this packet *before*
       // we actually send it for the first time (I think this is probably