Remove deprecated string features.

tests/standalone/io/secure_socket_test.dart

 // Copyright (c) 2012, 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.
 //
 // VMOptions=
 // VMOptions=--short_socket_read
 // VMOptions=--short_socket_write
 // VMOptions=--short_socket_read --short_socket_write
 
 import "dart:isolate";
 import "dart:io";
 
 void main() {
   ReceivePort keepAlive = new ReceivePort();
   SecureSocket.initialize();
   List<String> chunks = <String>[];
   SecureSocket.connect("www.google.dk", 443).then((socket) {
-    socket.add("GET / HTTP/1.0\r\nHost: www.google.dk\r\n\r\n".charCodes);
+    socket.add("GET / HTTP/1.0\r\nHost: www.google.dk\r\n\r\n".codeUnits);
     socket.close();
     socket.listen(
       (List<int> data) {
         var received = new String.fromCharCodes(data);
         chunks.add(received);
       },
       onDone: () {
         String fullPage = chunks.join();
         Expect.isTrue(fullPage.contains('</body></html>'));
         keepAlive.close();
       },
       onError: (e) => Expect.fail("Unexpected error $e"));
   });
 }