Don't count ERR_IO_PENDING as a QUIC write error code.

net/quic/quic_connection_helper.cc

 // 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.
 
 #include "net/quic/quic_connection_helper.h"
 
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/metrics/sparse_histogram.h"
 #include "base/task_runner.h"
@@ skipping 108 matching lines @@
   scoped_refptr<StringIOBuffer> buf(
       new StringIOBuffer(std::string(packet.data(),
                                      packet.length())));
   int rv = socket_->Write(buf.get(),
                           packet.length(),
                           base::Bind(&QuicConnectionHelper::OnWriteComplete,
                                      weak_factory_.GetWeakPtr()));
   if (rv >= 0) {
     *error = 0;
   } else {
-    UMA_HISTOGRAM_SPARSE_SLOWLY("Net.QuicSession.WriteError", -rv);
+    if (rv != ERR_IO_PENDING) {
+      UMA_HISTOGRAM_SPARSE_SLOWLY("Net.QuicSession.WriteError", -rv);
+    }
     *error = rv;
     rv = -1;
   }
   return rv;
 }
 
 bool QuicConnectionHelper::IsWriteBlockedDataBuffered() {
   // Chrome sockets' Write() methods buffer the data until the Write is
   // permitted.
   return true;
 }
 
 bool QuicConnectionHelper::IsWriteBlocked(int error) {
   return error == ERR_IO_PENDING;
 }
 
 QuicAlarm* QuicConnectionHelper::CreateAlarm(QuicAlarm::Delegate* delegate) {
   return new QuicChromeAlarm(clock_, task_runner_, delegate);
 }
 
 void QuicConnectionHelper::OnWriteComplete(int result) {
   // TODO(rch): Inform the connection about the result.
   connection_->OnCanWrite();
 }
 
 }  // namespace net