net/dns: Fix the last warning found by chromium-style clang plugin on Windows.

net/dns/dns_config_service_win.h

Index: net/dns/dns_config_service_win.h
diff --git a/net/dns/dns_config_service_win.h b/net/dns/dns_config_service_win.h
index 972d6efe86d045f8a156c9dced264d6e4997ec9b..5b6f22bb7de4b77b545fc22de1f37c3f8fa3bede 100644
--- a/net/dns/dns_config_service_win.h
+++ b/net/dns/dns_config_service_win.h
@@ -63,6 +63,9 @@ struct NET_EXPORT_PRIVATE DnsSystemSettings {
     RegDword level;
   };
 
+  DnsSystemSettings();
+  ~DnsSystemSettings();
+
   // Filled in by GetAdapterAddresses. Note that the alternative
   // GetNetworkParams does not include IPv6 addresses.
   scoped_ptr<IP_ADAPTER_ADDRESSES, base::FreeDeleter> addresses;