Some more removals of dart:utf.

pkg/http/lib/src/multipart_request.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_request;
 
 import 'dart:async';
+import 'dart:convert';
 import 'dart:math';
-import 'dart:utf';
 
 import 'base_request.dart';
 import 'byte_stream.dart';
 import 'multipart_file.dart';
 import 'utils.dart';
 
 /// A `multipart/form-data` request. Such a request has both string [fields],
 /// which function as normal form fields, and (potentially streamed) binary
 /// [files].
 ///
@@ skipping 35 matching lines @@
   List<MultipartFile> get files => _files;
 
   /// The total length of the request body, in bytes. This is calculated from
   /// [fields] and [files] and cannot be set manually.
   int get contentLength {
     var length = 0;
 
     fields.forEach((name, value) {
       length += "--".length + _BOUNDARY_LENGTH + "\r\n".length +
           _headerForField(name, value).length +
-          encodeUtf8(value).length + "\r\n".length;
+          UTF8.encode(value).length + "\r\n".length;
     });
 
     for (var file in _files) {
       length += "--".length + _BOUNDARY_LENGTH + "\r\n".length +
           _headerForFile(file).length +
           file.length + "\r\n".length;
     }
 
     return length + "--".length + _BOUNDARY_LENGTH + "--\r\n".length;
   }
@@ skipping 12 matching lines @@
     headers['content-transfer-encoding'] = 'binary';
     super.finalize();
 
     var controller = new StreamController<List<int>>(sync: true);
 
     void writeAscii(String string) {
       assert(isPlainAscii(string));
       controller.add(string.codeUnits);
     }
 
-    writeUtf8(String string) => controller.add(encodeUtf8(string));
+    writeUtf8(String string) => controller.add(UTF8.encode(string));
     writeLine() => controller.add([13, 10]); // \r\n
 
     fields.forEach((name, value) {
       writeAscii('--$boundary\r\n');
       writeAscii(_headerForField(name, value));
       writeUtf8(value);
       writeLine();
     });
 
     Future.forEach(_files, (file) {
@@ skipping 50 matching lines @@
   /// Returns a randomly-generated multipart boundary string
   String _boundaryString() {
     var prefix = "dart-http-boundary-";
     var list = new List<int>.generate(_BOUNDARY_LENGTH - prefix.length,
         (index) =>
             _BOUNDARY_CHARACTERS[_random.nextInt(_BOUNDARY_CHARACTERS.length)],
         growable: false);
     return "$prefix${new String.fromCharCodes(list)}";
   }
 }