Remove deprecated string features.

tests/standalone/io/secure_socket_bad_certificate_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_write --short_socket_read
 // The --short_socket_write option does not work with external server
 // www.google.dk.  Add this to the test when we have secure server sockets.
@@ skipping 31 matching lines @@
     Expect.isTrue(certificate.startValidity < new DateTime.now());
     Expect.isTrue(certificate.endValidity > new DateTime.now());
     return acceptCertificate;
   };
 
   return SecureSocket.connect(host,
                               443,
                               onBadCertificate: badCertificateCallback)
       .then((socket) {
         Expect.isTrue(acceptCertificate);
-        socket.add("GET / HTTP/1.0\r\nHost: $host\r\n\r\n".charCodes);
+        socket.add("GET / HTTP/1.0\r\nHost: $host\r\n\r\n".codeUnits);
         socket.close();
         return socket.reduce(<int>[], (message, data)  => message..addAll(data))
             .then((message) {
               String received = new String.fromCharCodes(message);
               Expect.isTrue(received.contains('</body></html>'));
             });
       }).catchError((e) {
         Expect.isFalse(acceptCertificate);
       });
 }