Remove deprecated string features.

pkg/http/test/client_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.
 
 library client_test;
 
 import 'dart:io';
 import 'dart:uri';
 
 import 'package:unittest/unittest.dart';
@@ skipping 23 matching lines @@
       }).whenComplete(client.close), completion(parse(equals({
         'method': 'POST',
         'path': '/',
         'headers': {
           'content-type': ['application/json; charset=utf-8'],
           'transfer-encoding': ['chunked']
         },
         'body': '{"hello": "world"}'
       }))));
 
-      request.sink.add('{"hello": "world"}'.charCodes);
+      request.sink.add('{"hello": "world"}'.codeUnits);
       request.sink.close();
     }), completes);
   });
 
   test('#send with an invalid URL', () {
     expect(startServer().then((_) {
       var client = new http.Client();
       var url = Uri.parse('http://http.invalid');
       var request = new http.StreamedRequest("POST", url);
       request.headers[HttpHeaders.CONTENT_TYPE] =
           'application/json; charset=utf-8';
 
       expect(client.send(request), throwsSocketIOException);
 
-      request.sink.add('{"hello": "world"}'.charCodes);
+      request.sink.add('{"hello": "world"}'.codeUnits);
       request.sink.close();
     }), completes);
   });
 }