Remove deprecated string features.

tests/standalone/io/secure_server_client_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.
 
 import "dart:io";
 import "dart:isolate";
 
 const SERVER_ADDRESS = "127.0.0.1";
 const HOST_NAME = "localhost";
 
 void WriteAndClose(Socket socket, String message) {
-  var data = message.charCodes;
+  var data = message.codeUnits;
   int written = 0;
   void write() {
     written += socket.writeList(data, written, data.length - written);
     if (written < data.length) {
       socket.onWrite = write;
     } else {
       socket.close(true);
     }
   }
   write();
@@ skipping 93 matching lines @@
   EndTest = () {
     Expect.equals(CLIENT_NAMES.length, server.numConnections);
     server.stop();
     keepAlive.close();
   };
 
   for (var x in CLIENT_NAMES) {
     new SecureTestClient(port, x);
   }
 }