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

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 79f0d5d25ecda3306082fc2ba7ce71c50e2f3ea0..3473472c787f1ed6d03fa986c6d3c5168ff79aba 100644
--- a/net/quic/quic_connection.cc
+++ b/net/quic/quic_connection.cc
@@ -18,6 +18,7 @@
 #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"
@@ -2073,7 +2074,13 @@ void QuicConnection::CloseConnection(QuicErrorCode error, bool from_peer) {
   }
   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 it after fix is merged.

[Alexei Svitkine (slow), 2016/02/01 19:03:14]

Planning to delete the histogram at that point too? If so, mention it here/

[ramant (doing other things), 2016/02/01 19:12:18]

Done.

+  if (visitor_) {
+    visitor_->OnConnectionClosed(error, from_peer);
+  } else {
+    UMA_HISTOGRAM_BOOLEAN("Net.QuicCloseConnection.NullVisitor", true);
+  }
   if (debug_visitor_ != nullptr) {
     debug_visitor_->OnConnectionClosed(error, from_peer);
   }