Avoid doing concurrent DNS resolves of the same hostname

net/ftp/ftp_network_layer.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_LAYER_H_
 #define NET_FTP_FTP_NETWORK_LAYER_H_
 
 #include "base/ref_counted.h"
 #include "net/ftp/ftp_transaction_factory.h"
 
 namespace net {
 
 class FtpNetworkSession;
 class FtpAuthCache;
+class HostResolver;
 
 class FtpNetworkLayer : public FtpTransactionFactory {
  public:
-  FtpNetworkLayer();
+  explicit FtpNetworkLayer(HostResolver* host_resolver);
   ~FtpNetworkLayer();
 
-  static FtpTransactionFactory* CreateFactory();
+  static FtpTransactionFactory* CreateFactory(HostResolver* host_resolver);
 
   // FtpTransactionFactory methods:
   virtual FtpTransaction* CreateTransaction();
   virtual void Suspend(bool suspend);
 
  private:
   scoped_refptr<FtpNetworkSession> session_;
   bool suspended_;
 };
 
 }  // namespace net
 
 #endif  // NET_FTP_FTP_NETWORK_LAYER_H_