Add logging to the QUIC write path.

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 9932032f0ac3b2b868dc9c615c9f08e6e8caa499..88bb2f13179d8021d20dddd9252e1ddc9fde263f 100644
--- a/net/quic/quic_connection.cc
+++ b/net/quic/quic_connection.cc
@@ -83,7 +83,7 @@ QuicConnection::QuicConnection(QuicGuid guid,
       write_blocked_(false),
       debug_visitor_(NULL),
       packet_creator_(guid_, &framer_, random_generator_, is_server),
-      packet_generator_(this, &packet_creator_),
+      packet_generator_(this, NULL, &packet_creator_),
       idle_network_timeout_(
           QuicTime::Delta::FromSeconds(kDefaultInitialTimeoutSecs)),
       overall_connection_timeout_(QuicTime::Delta::Infinite()),
@@ -1091,7 +1091,7 @@ bool QuicConnection::WritePacket(EncryptionLevel level,
 
   int error;
   QuicTime now = clock_->Now();
-  if (helper_->WritePacketToWire(*encrypted, &error) == -1) {
+  if (WritePacketToWire(sequence_number, level, *encrypted, &error) == -1) {
     if (helper_->IsWriteBlocked(error)) {
       // TODO(satyashekhar): It might be more efficient (fewer system calls), if
       // all connections share this variable i.e this becomes a part of
@@ -1136,6 +1136,18 @@ bool QuicConnection::WritePacket(EncryptionLevel level,
   return true;
 }
 
+int QuicConnection::WritePacketToWire(QuicPacketSequenceNumber sequence_number,
+                                      EncryptionLevel level,
+                                      const QuicEncryptedPacket& packet,
+                                      int* error) {
+  int rv = helper_->WritePacketToWire(packet, error);
+  if (debug_visitor_) {
+    debug_visitor_->OnPacketSent(sequence_number, level, packet,
+                                 rv == -1 ? *error : rv);

[eroman, 2013/06/20 22:20:04]

What is the range of |*error|?

Is it a NetError code? Is it a QuicError code? Is it something else?

This is important, since the code is assuming that *error can only be negative,
and is not -1. (Otherwise there is ambiguity with "rv" which is non-negative.

Please add some explanation in the comments at least, or choose a more
informative variable name.

[Ryan Hamilton, 2013/06/20 22:44:16]

-1 == error, otherwise positive values equal the number of bytes written.
Something else.  |error| will be set with a network error code in the event of
an error.
 
Change it to bytes_written and added a comment.

+  }
+  return rv;
+}
+
 bool QuicConnection::OnSerializedPacket(
     const SerializedPacket& serialized_packet) {
   if (serialized_packet.retransmittable_frames != NULL) {