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

net/quic/quic_connection.h

 // 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.
 //
 // The entity that handles framing writes for a Quic client or server.
 // Each QuicSession will have a connection associated with it.
 //
 // On the server side, the Dispatcher handles the raw reads, and hands off
 // packets via ProcessUdpPacket for framing and processing.
 //
@@ skipping 186 matching lines @@
   virtual void OnVersionNegotiationPacket(
       const QuicVersionNegotiationPacket& packet) {}
 
   // Called after a packet has been successfully parsed which results
   // in the revival of a packet via FEC.
   virtual void OnRevivedPacket(const QuicPacketHeader& revived_header,
                                base::StringPiece payload) {}
 
   // Called when the connection is closed.
   virtual void OnConnectionClosed(QuicErrorCode error, bool from_peer) {}
+
+  // Called when the version negotiation is successful.
+  virtual void OnSuccessfulVersionNegotiation(const QuicVersion& version) {}
 };
 
 class NET_EXPORT_PRIVATE QuicConnectionHelperInterface {
  public:
   virtual ~QuicConnectionHelperInterface() {}
 
   // Returns a QuicClock to be used for all time related functions.
   virtual const QuicClock* GetClock() const = 0;
 
   // Returns a QuicRandom to be used for all random number related functions.
@@ skipping 590 matching lines @@
   // If non-empty this contains the set of versions received in a
   // version negotiation packet.
   QuicVersionVector server_supported_versions_;
 
   DISALLOW_COPY_AND_ASSIGN(QuicConnection);
 };
 
 }  // namespace net
 
 #endif  // NET_QUIC_QUIC_CONNECTION_H_