Avoid doing concurrent DNS resolves of the same hostname

net/ftp/ftp_network_transaction.h

 // Copyright (c) 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.
 
 #ifndef NET_FTP_FTP_NETWORK_TRANSACTION_H_
 #define NET_FTP_FTP_NETWORK_TRANSACTION_H_
 
 #include <string>
 
 #include "base/ref_counted.h"
@@ skipping 124 matching lines @@
   Command command_sent_;
 
   CompletionCallbackImpl<FtpNetworkTransaction> io_callback_;
   CompletionCallback* user_callback_;
 
   scoped_refptr<FtpNetworkSession> session_;
 
   const FtpRequestInfo* request_;
   FtpResponseInfo response_;
 
-  HostResolver resolver_;
+  // Cancels the outstanding request on destruction.
+  SingleRequestHostResolver resolver_;
   AddressList addresses_;
 
   // User buffer and length passed to the Read method.
   scoped_refptr<IOBuffer> read_ctrl_buf_;
   int read_ctrl_buf_size_;
 
   scoped_refptr<IOBuffer> response_message_buf_;
   int response_message_buf_len_;
 
   scoped_refptr<IOBuffer> read_data_buf_;
@@ skipping 46 matching lines @@
     STATE_DATA_READ,
     STATE_DATA_READ_COMPLETE,
     STATE_NONE
   };
   State next_state_;
 };
 
 }  // namespace net
 
 #endif  // NET_FTP_FTP_NETWORK_TRANSACTION_H_