[net/dns] Add test DualFamilyLocalhost and fix it when DnsClient enabled.

net/dns/host_resolver_proc.h

 // 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.
 
 #ifndef NET_DNS_HOST_RESOLVER_PROC_H_
 #define NET_DNS_HOST_RESOLVER_PROC_H_
 
 #include <string>
 
 #include "base/memory/ref_counted.h"
@@ skipping 74 matching lines @@
 // network error code, and fills |os_error| with a more specific error if it
 // was non-NULL.
 NET_EXPORT_PRIVATE int SystemHostResolverCall(
     const std::string& host,
     AddressFamily address_family,
     HostResolverFlags host_resolver_flags,
     AddressList* addrlist,
     int* os_error);
 
 // Wraps call to SystemHostResolverCall as an instance of HostResolverProc.
-class SystemHostResolverProc : public HostResolverProc {
+class NET_EXPORT_PRIVATE SystemHostResolverProc : public HostResolverProc {
  public:
   SystemHostResolverProc();
   virtual int Resolve(const std::string& hostname,
                       AddressFamily address_family,
                       HostResolverFlags host_resolver_flags,
                       AddressList* addr_list,
                       int* os_error) OVERRIDE;
  protected:
   virtual ~SystemHostResolverProc();
 
   DISALLOW_COPY_AND_ASSIGN(SystemHostResolverProc);
 };
 
 }  // namespace net
 
 #endif  // NET_DNS_HOST_RESOLVER_PROC_H_