[net/dns] Resolve AF_UNSPEC on dual-stacked systems. Sort addresses according to RFC3484.

net/dns/dns_client.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_DNS_CLIENT_H_
 #define NET_DNS_DNS_CLIENT_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "net/base/net_export.h"
 
 namespace net {
 
+class AddressSorter;
 struct DnsConfig;
 class DnsTransactionFactory;
 class NetLog;
 
-// Convenience wrapper allows easy injection of DnsTransaction into
-// HostResolverImpl.
+// Convenience wrapper which allows easy injection of DnsTransaction into
+// HostResolverImpl. Pointers returned by the Get* methods are only guaranteed
+// to remain valid until next time SetConfig is called.
 class NET_EXPORT DnsClient {
  public:
   virtual ~DnsClient() {}
 
   // Creates a new DnsTransactionFactory according to the new |config|.
   virtual void SetConfig(const DnsConfig& config) = 0;
 
   // Returns NULL if the current config is not valid.
   virtual const DnsConfig* GetConfig() const = 0;
 
   // Returns NULL if the current config is not valid.
   virtual DnsTransactionFactory* GetTransactionFactory() = 0;
 
+  // Returns NULL if the current config is not valid.
+  virtual AddressSorter* GetAddressSorter() = 0;
+
   // Creates default client.
   static scoped_ptr<DnsClient> CreateClient(NetLog* net_log);
 };
 
 }  // namespace net
 
 #endif  // NET_DNS_DNS_CLIENT_H_