QUIC - Fix for crash in stable channel. Check for null |visitor_| before

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>
 #include <iterator>
 #include <limits>
 #include <memory>
 #include <set>
 #include <utility>
 
 #include "base/format_macros.h"
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/stl_util.h"
 #include "base/strings/stringprintf.h"
 #include "net/base/net_errors.h"
 #include "net/quic/crypto/crypto_protocol.h"
 #include "net/quic/crypto/quic_decrypter.h"
 #include "net/quic/crypto/quic_encrypter.h"
 #include "net/quic/proto/cached_network_parameters.pb.h"
 #include "net/quic/quic_bandwidth.h"
 #include "net/quic/quic_bug_tracker.h"
 #include "net/quic/quic_config.h"
@@ skipping 2035 matching lines @@
   packet_generator_.FlushAllQueuedFrames();
 }
 
 void QuicConnection::CloseConnection(QuicErrorCode error, bool from_peer) {
   if (!connected_) {
     DVLOG(1) << "Connection is already closed.";
     return;
   }
   connected_ = false;
   DCHECK(visitor_ != nullptr);
-  visitor_->OnConnectionClosed(error, from_peer);
+  // TODO(rtenneti): crbug.com/546668. A temporary fix. Added a check for null
+  // |visitor_| to fix crash bug. Delete |visitor_| check and histogram after
+  // fix is merged.
+  if (visitor_) {

[Alexander Potapenko, 2016/02/07 08:40:18]

Drive-by nit: this check is inconsistent with other nullptr checks in the file.

[ramant (doing other things), 2016/02/09 00:10:34]

Done. Uploaded the following CL. Thanks.
 
https://codereview.chromium.org/1679113002/

+    visitor_->OnConnectionClosed(error, from_peer);
+  } else {
+    UMA_HISTOGRAM_BOOLEAN("Net.QuicCloseConnection.NullVisitor", true);
+  }
   if (debug_visitor_ != nullptr) {
     debug_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();
@@ skipping 354 matching lines @@
 void QuicConnection::OnPathClosed(QuicPathId path_id) {
   // Stop receiving packets on this path.
   framer_.OnPathClosed(path_id);
 }
 
 bool QuicConnection::ack_frame_updated() const {
   return received_packet_manager_.ack_frame_updated();
 }
 
 }  // namespace net