Remove private system API calls in dns_config_service_posix on iOS

net/dns/dns_config_watcher_mac.h

+// Copyright 2014 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.
+
+#include "base/callback_forward.h"
+#include "net/dns/dns_config_service_posix.h"
+#include "net/dns/notify_watcher_mac.h"
+
+namespace net {
+namespace internal {
+
+// Watches DNS configuration on Mac.
+class DnsConfigWatcher {
+ public:
+  bool Watch(const base::Callback<void(bool succeeded)>& callback);
+
+  // Returns an error if the DNS configuration is invalid.
+  // Returns CONFIG_PARSE_POSIX_OK otherwise.
+  static ConfigParsePosixResult CheckDnsConfig();
+
+ private:
+  NotifyWatcherMac watcher_;
+};
+
+}  // naespace internal
+}  // namespace net