Remove Sink and move CollectionSink to async.

pkg/http/lib/src/multipart_request.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_request;
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:math';
 import 'dart:uri';
@@ skipping 55 matching lines @@
         "multipart requests.");
   }
 
   /// The form fields to send for this request.
   final Map<String, String> fields;
 
   /// The sink for files to upload for this request.
   ///
   /// This doesn't need to be closed. When the request is sent, whichever files
   /// are written to this sink at that point will be used.
-  Sink<MultipartFile> get files => _files;
+  StreamSink<MultipartFile> get files => _files;
 
   /// The private version of [files], typed so that the underlying collection is
   /// accessible.
   final CollectionSink<MultipartFile> _files;
 
   /// Creates a new [MultipartRequest].
   MultipartRequest(String method, Uri url)
     : super(method, url),
       fields = {},
       _files = new CollectionSink<MultipartFile>(<MultipartFile>[]);
@@ skipping 79 matching lines @@
   String _boundaryString(int length) {
     var prefix = "dart-http-boundary-";
     var list = new List<int>.fixedLength(length - prefix.length);
     for (var i = 0; i < list.length; i++) {
       list[i] = _BOUNDARY_CHARACTERS[
           _random.nextInt(_BOUNDARY_CHARACTERS.length)];
     }
     return "$prefix${new String.fromCharCodes(list)}";
   }
 }