Add reverse dns lookup as a method on InternetAddress.

tests/standalone/io/internet_address_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 "package:expect/expect.dart";
 
 void testDefaultAddresses() {
   var loopback4 = InternetAddress.LOOPBACK_IP_V4;
@@ skipping 14 matching lines @@
   Expect.equals("0.0.0.0", any4.host);
   Expect.equals("0.0.0.0", any4.address);
 
   var any6 = InternetAddress.ANY_IP_V6;
   Expect.isNotNull(any6);
   Expect.equals(InternetAddressType.IP_V6, any6.type);
   Expect.equals("::", any6.host);
   Expect.equals("::", any6.address);
 }
 
+void testReverseLookup() {
+  InternetAddress.lookup('localhost').then((addrs) {
+    addrs.first.reverse().then((addr) {
+      Expect.equals('localhost', addr.host);
+    });
+  });
+
+  InternetAddress.lookup('127.0.0.1').then((addrs) {
+    addrs.first.reverse().then((addr) {
+      Expect.equals('localhost', addr.host);
+    });
+  });
+}
+
 void main() {
   testDefaultAddresses();
+  testReverseLookup();
 }