Log the quic version for internal server tracing. Not used in production.

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 a9ad334afa64dafb62b1afc9d5d72aae029e8380..3ca6d9945efbefa49281e4eede2006e3d2f6979d 100644
--- a/net/quic/quic_connection.cc
+++ b/net/quic/quic_connection.cc
@@ -365,6 +365,9 @@ bool QuicConnection::OnProtocolVersionMismatch(QuicVersion received_version) {
 
   version_negotiation_state_ = NEGOTIATED_VERSION;
   visitor_->OnSuccessfulVersionNegotiation(received_version);
+  if (debug_visitor_.get() != NULL) {
+    debug_visitor_->OnSuccessfulVersionNegotiation(received_version);
+  }
   DVLOG(1) << ENDPOINT << "version negotiated " << received_version;
 
   // Store the new version.
@@ -491,6 +494,9 @@ bool QuicConnection::OnPacketHeader(const QuicPacketHeader& header) {
         DCHECK_EQ(header.public_header.versions[0], version());
         version_negotiation_state_ = NEGOTIATED_VERSION;
         visitor_->OnSuccessfulVersionNegotiation(version());
+        if (debug_visitor_.get() != NULL) {
+          debug_visitor_->OnSuccessfulVersionNegotiation(version());
+        }
       }
     } else {
       DCHECK(!header.public_header.version_flag);
@@ -499,6 +505,9 @@ bool QuicConnection::OnPacketHeader(const QuicPacketHeader& header) {
       packet_generator_.StopSendingVersion();
       version_negotiation_state_ = NEGOTIATED_VERSION;
       visitor_->OnSuccessfulVersionNegotiation(version());
+      if (debug_visitor_.get() != NULL) {
+        debug_visitor_->OnSuccessfulVersionNegotiation(version());
+      }
     }
   }