Avoid doing concurrent DNS resolves of the same hostname

net/http/http_network_transaction.cc

 // Copyright (c) 2006-2008 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/http/http_network_transaction.h"
 
 #include "base/scoped_ptr.h"
 #include "base/compiler_specific.h"
 #include "base/field_trial.h"
 #include "base/string_util.h"
 #include "base/trace_event.h"
 #include "build/build_config.h"
 #include "net/base/client_socket_factory.h"
 #include "net/base/connection_type_histograms.h"
 #include "net/base/dns_resolution_observer.h"
-#include "net/base/host_resolver.h"
 #include "net/base/io_buffer.h"
 #include "net/base/load_flags.h"
 #include "net/base/net_errors.h"
 #include "net/base/net_util.h"
 #include "net/base/ssl_client_socket.h"
 #include "net/base/upload_data_stream.h"
 #include "net/http/http_auth.h"
 #include "net/http/http_auth_handler.h"
 #include "net/http/http_basic_stream.h"
 #include "net/http/http_chunked_decoder.h"
@@ skipping 1600 matching lines @@
     host_and_port = proxy_info_.proxy_server().host_and_port();
   } else {
     DCHECK(target == HttpAuth::AUTH_SERVER);
     host_and_port = GetHostAndPort(request_->url);
   }
   auth_info->host_and_port = ASCIIToWide(host_and_port);
   response_.auth_challenge = auth_info;
 }
 
 }  // namespace net