Add varz to track QUIC packets and bytes sent by transmission type.

net/quic/quic_packet_generator.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.
 //
 // Responsible for generating packets on behalf of a QuicConnection.
 // Packets are serialized just-in-time.  Control frames are queued.
 // Ack and Feedback frames will be requested from the Connection
 // just-in-time.  When a packet needs to be sent, the Generator
 // will serialize a packet and pass it to QuicConnection::SendOrQueuePacket()
 //
@@ skipping 65 matching lines @@
   };
 
   // Interface which gets callbacks from the QuicPacketGenerator at interesting
   // points.  Implementations must not mutate the state of the generator
   // as a result of these callbacks.
   class NET_EXPORT_PRIVATE DebugDelegateInterface {
    public:
     virtual ~DebugDelegateInterface() {}
 
     // Called when a frame has been added to the current packet.
-    virtual void OnFrameAddedToPacket(const QuicFrame& frame) = 0;
+    virtual void OnFrameAddedToPacket(const QuicFrame& frame) {}
   };
 
   QuicPacketGenerator(DelegateInterface* delegate,
                       DebugDelegateInterface* debug_delegate,
                       QuicPacketCreator* creator);
 
   virtual ~QuicPacketGenerator();
 
   // Indicates that an ACK frame should be sent.  If |also_send_feedback| is
   // true, then it also indicates a CONGESTION_FEEDBACK frame should be sent.
@@ skipping 74 matching lines @@
   scoped_ptr<QuicAckFrame> pending_ack_frame_;
   scoped_ptr<QuicCongestionFeedbackFrame> pending_feedback_frame_;
   scoped_ptr<QuicStopWaitingFrame> pending_stop_waiting_frame_;
 
   DISALLOW_COPY_AND_ASSIGN(QuicPacketGenerator);
 };
 
 }  // namespace net
 
 #endif  // NET_QUIC_QUIC_PACKET_GENERATOR_H_