Rip out dart:io from pkg/http wherever possible.

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';
 
@@ skipping 11 matching lines @@
 /// This request automatically sets the Content-Type header to
 /// `multipart/form-data` and the Content-Transfer-Encoding header to `binary`.
 /// These values will override any values set by the user.
 ///
 ///     var uri = Uri.parse("http://pub.dartlang.org/packages/create");
 ///     var request = new http.MultipartRequest("POST", url);
 ///     request.fields['user'] = 'nweiz@google.com';
 ///     request.files.add(new http.MultipartFile.fromFile(
 ///         'package',
 ///         new File('build/package.tar.gz'),
-///         contentType: new ContentType('application', 'x-tar'));
+///         contentType: new MediaType('application', 'x-tar'));
 ///     request.send().then((response) {
 ///       if (response.statusCode == 200) print("Uploaded!");
 ///     });
 class MultipartRequest extends BaseRequest {
   /// The total length of the multipart boundaries used when building the
   /// request body. According to http://tools.ietf.org/html/rfc1341.html, this
   /// can't be longer than 70.
   static const int _BOUNDARY_LENGTH = 70;
 
   static final Random _random = new Random();
@@ skipping 124 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)}";
   }
 }