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

net/dns/dns_config_service.h

Index: net/dns/dns_config_service.h
diff --git a/net/dns/dns_config_service.h b/net/dns/dns_config_service.h
index 4babb9e7d37903aac0e439bb76baf857fed20fe7..d14a2cd66fa9b7b218dccd4e6bed4d913f657861 100644
--- a/net/dns/dns_config_service.h
+++ b/net/dns/dns_config_service.h
@@ -59,6 +59,10 @@ struct NET_EXPORT_PRIVATE DnsConfig {
 
   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;