Avoid doing concurrent DNS resolves of the same hostname

net/ftp/ftp_network_session.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_SESSION_H_
 #define NET_FTP_FTP_NETWORK_SESSION_H_
 
 #include "base/ref_counted.h"
 #include "net/ftp/ftp_auth_cache.h"
 
 namespace net {
 
+class HostResolver;
+
 // This class holds session objects used by FtpNetworkTransaction objects.
 class FtpNetworkSession : public base::RefCounted<FtpNetworkSession> {
  public:
-  FtpNetworkSession() {}
+  explicit FtpNetworkSession(HostResolver* host_resolver)
+      : host_resolver_(host_resolver) {}
 
+  HostResolver* host_resolver() { return host_resolver_; }
   FtpAuthCache* auth_cache() { return &auth_cache_; }
 
  private:
+  HostResolver* host_resolver_;
   FtpAuthCache auth_cache_;
 };
 
 }  // namespace net
 
 #endif  // NET_FTP_FTP_NETWORK_SESSION_H_