Introduce UMA metrics for path MTU discovery.

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 425 matching lines @@
     packet_generator_.set_debug_delegate(debug_visitor);
     sent_packet_manager_.set_debug_delegate(debug_visitor);
   }
   const IPEndPoint& self_address() const { return self_address_; }
   const IPEndPoint& peer_address() const { return peer_address_; }
   QuicConnectionId connection_id() const { return connection_id_; }
   const QuicClock* clock() const { return clock_; }
   QuicRandom* random_generator() const { return random_generator_; }
   QuicByteCount max_packet_length() const;
   void set_max_packet_length(QuicByteCount length);
+  size_t mtu_probe_count() const { return mtu_probe_count_; }
 
   bool connected() const { return connected_; }
 
   // Must only be called on client connections.
   const QuicVersionVector& server_supported_versions() const {
     DCHECK_EQ(Perspective::IS_CLIENT, perspective_);
     return server_supported_versions_;
   }
 
   size_t NumFecGroups() const { return group_map_.size(); }
@@ skipping 478 matching lines @@
 
   // The size of the largest packet received from peer.
   QuicByteCount largest_received_packet_size_;
 
   DISALLOW_COPY_AND_ASSIGN(QuicConnection);
 };
 
 }  // namespace net
 
 #endif  // NET_QUIC_QUIC_CONNECTION_H_