Remove deprecated string features.

tests/standalone/io/secure_client_raw_server_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.
 //
 // VMOptions=
 // VMOptions=--short_socket_read
 // VMOptions=--short_socket_write
 // VMOptions=--short_socket_read --short_socket_write
 
 import "dart:async";
@@ skipping 43 matching lines @@
       });
     });
     return server;
   });
 }
 
 Future testClient(server) {
   Completer success = new Completer();
   List<String> chunks = <String>[];
   SecureSocket.connect(HOST_NAME, server.port).then((socket) {
-    socket.add("Hello server.".charCodes);
+    socket.add("Hello server.".codeUnits);
     socket.close();
     socket.listen(
       (List<int> data) {
         var received = new String.fromCharCodes(data);
         chunks.add(received);
       },
       onDone: () {
         String reply = chunks.join();
         Expect.equals("Hello server.", reply);
         success.complete(server);
       });
   });
   return success.future;
 }
 
 void main() {
   Path scriptDir = new Path(new Options().script).directoryPath;
   Path certificateDatabase = scriptDir.append('pkcert');
   SecureSocket.initialize(database: certificateDatabase.toNativePath(),
                           password: 'dartdart');
 
   startEchoServer()
       .then(testClient)
       .then((server) {
         server.close();
       });
 }