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

net/dns/address_sorter.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_ADDRESS_SORTER_H_
+#define NET_DNS_ADDRESS_SORTER_H_
+#pragma once
+
+#include "base/basictypes.h"
+#include "base/memory/scoped_ptr.h"
+
+namespace net {
+
+class AddressList;
+
+class AddressSorter {
+ public:
+  virtual ~AddressSorter() {}
+
+  // Sorts |list| according to revised RFC3484.
+  virtual bool Sort(AddressList* list) const = 0;
+
+  // Creates platform-dependent AddressSorter.
+  static scoped_ptr<AddressSorter> CreateAddressSorter();
+};
+
+}  // namespace net
+
+#endif  // NET_DNS_ADDRESS_SORTER_H_