Fix strong mode errors in dart:io.

sdk/lib/io/socket.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.
 
 part of dart.io;
 
 
 /**
  * [InternetAddressType] is the type an [InternetAddress]. Currently,
  * IP version 4 (IPv4) and IP version 6 (IPv6) are supported.
@@ skipping 123 matching lines @@
    * Lookup a host, returning a Future of a list of
    * [InternetAddress]s. If [type] is [InternetAddressType.ANY], it
    * will lookup both IP version 4 (IPv4) and IP version 6 (IPv6)
    * addresses. If [type] is either [InternetAddressType.IP_V4] or
    * [InternetAddressType.IP_V6] it will only lookup addresses of the
    * specified type. The order of the list can, and most likely will,
    * change over time.
    */
   external static Future<List<InternetAddress>> lookup(
       String host, {InternetAddressType type: InternetAddressType.ANY});
+
+  /**
+   * Clones the given [address] with the new [host].
+   *
+   * The [address] must be an [InternetAddress] that was created with one
+   * of the static methods of this class.
+   */
+  external static InternetAddress _cloneWithNewHost(
+      InternetAddress address, String host);
 }
 
 
 /**
  * A [NetworkInterface] represents an active network interface on the current
  * system. It contains a list of [InternetAddress]es that are bound to the
  * interface.
  */
 abstract class NetworkInterface {
   /**
@@ skipping 566 matching lines @@
     }
     if (address != null) {
       sb.write(", address = ${address.host}");
     }
     if (port != null) {
       sb.write(", port = $port");
     }
     return sb.toString();
   }
 }