Low-impact. Dispatcher now uses QuicServerSession, not QuicSession.

net/quic/quic_connection.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "net/quic/quic_connection.h"
 
 #include <string.h>
 #include <sys/types.h>
 
 #include <algorithm>
@@ skipping 1887 matching lines @@
 void QuicConnection::CloseConnection(QuicErrorCode error, bool from_peer) {
   if (!connected_) {
     DLOG(DFATAL) << "Error: attempt to close an already closed connection"
                  << base::debug::StackTrace().ToString();
     return;
   }
   connected_ = false;
   if (debug_visitor_ != nullptr) {
     debug_visitor_->OnConnectionClosed(error, from_peer);
   }
+  DCHECK(visitor_ != nullptr);
   visitor_->OnConnectionClosed(error, from_peer);
   // Cancel the alarms so they don't trigger any action now that the
   // connection is closed.
   ack_alarm_->Cancel();
   ping_alarm_->Cancel();
   fec_alarm_->Cancel();
   resume_writes_alarm_->Cancel();
   retransmission_alarm_->Cancel();
   send_alarm_->Cancel();
   timeout_alarm_->Cancel();
@@ skipping 207 matching lines @@
   }
   for (const QuicFrame& frame : retransmittable_frames->frames()) {
     if (frame.type == CONNECTION_CLOSE_FRAME) {
       return true;
     }
   }
   return false;
 }
 
 }  // namespace net