Detect domain-specific resolvers on OS X and disable DnsClient in such cases.

net/dns/dns_config_service.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_CONFIG_SERVICE_H_
 #define NET_DNS_DNS_CONFIG_SERVICE_H_
 
 #include <map>
 #include <string>
 #include <vector>
@@ skipping 41 matching lines @@
   }
 
   // List of name server addresses.
   std::vector<IPEndPoint> nameservers;
   // Suffix search list; used on first lookup when number of dots in given name
   // is less than |ndots|.
   std::vector<std::string> search;
 
   DnsHosts hosts;
 
+  // True if there are options set in the system configuration that are not yet
+  // supported by DnsClient.
+  bool unhandled_options;
+
   // AppendToMultiLabelName: is suffix search performed for multi-label names?
   // True, except on Windows where it can be configured.
   bool append_to_multi_label_name;
 
   // Indicates that source port randomization is required. This uses additional
   // resources on some platforms.
   bool randomize_ports;
 
   // Resolver options; see man resolv.conf.
 
@@ skipping 93 matching lines @@
 
   // Started in Invalidate*, cleared in On*Read.
   base::OneShotTimer<DnsConfigService> timer_;
 
   DISALLOW_COPY_AND_ASSIGN(DnsConfigService);
 };
 
 }  // namespace net
 
 #endif  // NET_DNS_DNS_CONFIG_SERVICE_H_