Add static getters for common internet addresses

tests/standalone/io/socket_ipv6_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:io';
 import 'dart:isolate';
 
 const ANY = InternetAddressType.ANY;
 
 void testIPv6toIPv6() {
@@ skipping 49 matching lines @@
       socket.destroy();
     });
   });
 }
 
 void testIPv6Lookup() {
   var port = new ReceivePort();
   InternetAddress.lookup("::0", type: ANY).then((list) {
     if (list.length < 0) throw "no address";
     for (var entry in list) {
-      if (entry.type != InternetAddressType.IPv6) {
+      if (entry.type != InternetAddressType.IP_V6) {
         throw "Wrong IP type";
       }
     }
     port.close();
   });
 }
 
 void testIPv4Lookup() {
   var port = new ReceivePort();
   InternetAddress.lookup("127.0.0.1").then((list) {
     if (list.length < 0) throw "no addresse";
     for (var entry in list) {
-      if (entry.type != InternetAddressType.IPv4) {
+      if (entry.type != InternetAddressType.IP_V4) {
         throw "Wrong IP type";
       }
     }
     port.close();
   });
 }
 
 void main() {
   testIPv6toIPv6();
   testIPv4toIPv6();
   testIPv6toIPv4();
   testIPv4toIPv4();
   testIPv6Lookup();
   testIPv4Lookup();
 }