Refactor QuicConnection's async write behavior to record a packet as

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 ffdea9bc449eba38e33bb3cfe8b945aead0bcd3e..41221ccee2dd25daf69556aff1df6b6a5b37b281 100644
--- a/net/quic/quic_sent_packet_manager.cc
+++ b/net/quic/quic_sent_packet_manager.cc
@@ -520,15 +520,11 @@ bool QuicSentPacketManager::OnPacketSent(
     TransmissionType transmission_type,
     HasRetransmittableData has_retransmittable_data) {
   DCHECK_LT(0u, sequence_number);
+  DCHECK(unacked_packets_.IsUnacked(sequence_number));
   LOG_IF(DFATAL, bytes == 0) << "Cannot send empty packets.";
   if (pending_timer_transmission_count_ > 0) {
     --pending_timer_transmission_count_;
   }
-  // In rare circumstances, the packet could be serialized, sent, and then acked
-  // before OnPacketSent is called.
-  if (!unacked_packets_.IsUnacked(sequence_number)) {
-    return false;
-  }
 
   if (unacked_packets_.bytes_in_flight() == 0) {
     // TODO(ianswett): Consider being less aggressive to force a new