Remove deprecated string features.

tests/standalone/io/socket_close_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
 //
 // Test socket close events.
@@ skipping 83 matching lines @@
       socket.close();
     }
 
     void connectHandler(socket) {
       socket.listen(
           dataHandler,
           onDone: () => closeHandler(socket),
           onError: (error) => errorHandler(socket));
 
       void writeHello() {
-        socket.add("Hello".charCodes);
+        socket.add("Hello".codeUnits);
       }
 
       _iterations++;
       switch (_mode) {
         case 0:
           socket.destroy();
           proceed();
           break;
         case 1:
           writeHello();
@@ skipping 102 matching lines @@
 
     void readBytes(bytes, whenFiveBytes) {
       data.readBytes += bytes.length;
       Expect.isTrue(data.readBytes <= 5);
       if (data.readBytes == 5) {
         whenFiveBytes();
       }
     }
 
     void writeHello() {
-      connection.add("Hello".charCodes);
+      connection.add("Hello".codeUnits);
     }
 
     void dataHandler(bytes) {
       switch (_mode) {
         case 0:
           Expect.fail("No data expected");
           break;
         case 1:
           readBytes(bytes, () { _dataEvents++; });
           break;
@@ skipping 139 matching lines @@
   var tests = 7;
   var port = new ReceivePort();
   var completed = 0;
   port.receive((message, ignore) {
     if (++completed == tests) port.close();
   });
   for (var i = 0; i < tests; i++) {
     new SocketClose.start(i, port.toSendPort());
   }
 }