Some more removals of dart:utf.

pkg/http/test/multipart_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 multipart_test;
 
 import 'dart:async';
+import 'dart:convert';
 import 'dart:io';
-import 'dart:utf';
 
 import 'package:http/http.dart' as http;
 import 'package:path/path.dart' as path;
 import 'package:unittest/unittest.dart';
 
 import 'utils.dart';
 
 /// A matcher that validates the body of a multipart request after finalization.
 /// The string "{{boundary}}" in [pattern] will be replaced by the boundary
 /// string for the request, and LF newlines will be replaced with CRLF.
 /// Indentation will be normalized.
 Matcher bodyMatches(String pattern) => new _BodyMatches(pattern);
 
 class _BodyMatches extends Matcher {
   final String _pattern;
 
   _BodyMatches(this._pattern);
 
   bool matches(item, Map matchState) {
     if (item is! http.MultipartRequest) return false;
 
     var future = item.finalize().toBytes().then((bodyBytes) {
-      var body = decodeUtf8(bodyBytes);
+      var body = UTF8.decode(bodyBytes);
       var contentType = ContentType.parse(item.headers['content-type']);
       var boundary = contentType.parameters['boundary'];
       var expected = cleanUpLiteral(_pattern)
           .replaceAll("\n", "\r\n")
           .replaceAll("{{boundary}}", boundary);
 
       expect(body, equals(expected));
       expect(item.contentLength, equals(bodyBytes.length));
     });
 
@@ skipping 181 matching lines @@
         content-type: application/octet-stream
         content-disposition: form-data; name="file"; filename="test-file"
 
         hello
         --{{boundary}}--
         '''));
       }), completes);
     });
   });
 }