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

pkg/http/lib/src/multipart_file.dart

 // Copyright (c) 2012, 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_file;
 
 import 'dart:async';
+import 'dart:io';
 import 'dart:convert';
-import 'dart:io';
 
+import 'package:http_parser/http_parser.dart';
 import 'package:path/path.dart' as path;
 import 'package:stack_trace/stack_trace.dart';
 
 import 'byte_stream.dart';
 import 'utils.dart';
 
 /// A file to be uploaded as part of a [MultipartRequest]. This doesn't need to
 /// correspond to a physical file.
 class MultipartFile {
   /// The name of the form field for the file.
   final String field;
 
   /// The size of the file in bytes. This must be known in advance, even if this
   /// file is created from a [ByteStream].
   final int length;
 
   /// The basename of the file. May be null.
   final String filename;
 
   /// The content-type of the file. Defaults to `application/octet-stream`.
-  final ContentType contentType;
+  final MediaType contentType;
 
   /// The stream that will emit the file's contents.
   final ByteStream _stream;
 
   /// Whether [finalize] has been called.
   bool get isFinalized => _isFinalized;
   bool _isFinalized = false;
 
   /// Creates a new [MultipartFile] from a chunked [Stream] of bytes. The length
   /// of the file in bytes must be known in advance. If it's not, read the data
   /// from the stream and use [MultipartFile.fromBytes] instead.
   ///
   /// [contentType] currently defaults to `application/octet-stream`, but in the
   /// future may be inferred from [filename].
   MultipartFile(this.field, Stream<List<int>> stream, this.length,
-      {this.filename, ContentType contentType})
+      {this.filename, MediaType contentType})
     : this._stream = toByteStream(stream),
       this.contentType = contentType != null ? contentType :
-          new ContentType("application", "octet-stream");
+          new MediaType("application", "octet-stream");
 
   /// Creates a new [MultipartFile] from a byte array.
   ///
   /// [contentType] currently defaults to `application/octet-stream`, but in the
   /// future may be inferred from [filename].
   factory MultipartFile.fromBytes(String field, List<int> value,
-      {String filename, ContentType contentType}) {
+      {String filename, MediaType contentType}) {
     var stream = new ByteStream.fromBytes(value);
     return new MultipartFile(field, stream, value.length,
         filename: filename,
         contentType: contentType);
   }
 
   /// Creates a new [MultipartFile] from a string.
   ///
   /// The encoding to use when translating [value] into bytes is taken from
   /// [contentType] if it has a charset set. Otherwise, it defaults to UTF-8.
   /// [contentType] currently defaults to `text/plain; charset=utf-8`, but in
   /// the future may be inferred from [filename].
   factory MultipartFile.fromString(String field, String value,
-      {String filename, ContentType contentType}) {
-    contentType = contentType == null ? new ContentType("text", "plain")
+      {String filename, MediaType contentType}) {
+    contentType = contentType == null ? new MediaType("text", "plain")
                                       : contentType;
-    var charset = contentType.charset;
-    var encoding = encodingForCharset(contentType.charset, UTF8);
-    // Make a new contentType with ensured charset.
-    contentType = new ContentType(contentType.primaryType,
-                                  contentType.subType,
-                                  charset: encoding.name,
-                                  parameters: contentType.parameters);
+    var encoding = encodingForCharset(contentType.parameters['charset'], UTF8);
+    contentType = contentType.change(parameters: {'charset': encoding.name});
 
     return new MultipartFile.fromBytes(field, encoding.encode(value),
         filename: filename,
         contentType: contentType);
   }
 
   // TODO(nweiz): Infer the content-type from the filename.
   /// Creates a new [MultipartFile] from a path to a file on disk.
   ///
   /// [filename] defaults to the basename of [filePath]. [contentType] currently
   /// defaults to `application/octet-stream`, but in the future may be inferred
   /// from [filename].
   static Future<MultipartFile> fromPath(String field, String filePath,
-      {String filename, ContentType contentType}) {
+      {String filename, MediaType contentType}) {
     if (filename == null) filename = path.basename(filePath);
     var file = new File(filePath);
     return Chain.track(file.length()).then((length) {
       var stream = new ByteStream(Chain.track(file.openRead()));
       return new MultipartFile(field, stream, length,
           filename: filename,
           contentType: contentType);
     });
   }
 
   // Finalizes the file in preparation for it being sent as part of a
   // [MultipartRequest]. This returns a [ByteStream] that should emit the body
   // of the file. The stream may be closed to indicate an empty file.
   ByteStream finalize() {
     if (isFinalized) {
       throw new StateError("Can't finalize a finalized MultipartFile.");
     }
     _isFinalized = true;
     return _stream;
   }
 }