Fix type checking of void type.

runtime/bin/mime_multipart_parser.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.
 
 /**
  * Parser for MIME multipart types of data as described in RFC 2046
  * section 5.1.1. The data to parse is supplied through the [:update:]
  * method. As the data is parsed the following callbacks are called:
  *
  *   [:partStart;
@@ skipping 35 matching lines @@
     _boundary[0] = _CharCode.CR;
     _boundary[1] = _CharCode.LF;
     _boundary[2] = _CharCode.DASH;
     _boundary[3] = _CharCode.DASH;
     _boundary.setRange(4, charCodes.length, charCodes);
     _state = _START;
     _headerField = new StringBuffer();
     _headerValue = new StringBuffer();
   }
 
-  void update(List<int> buffer, int offset, int count) {
+  int update(List<int> buffer, int offset, int count) {
     // Current index in the data buffer. If index is negative then it
     // is the index into the artificial prefix of the boundary string.
     int index;
     // Number of boundary bytes to artificially place before the supplied data.
     int boundaryPrefix = 0;
     // Position where content starts. Will be null if no known content
     // start exists. Will be negative of the content starts in the
     // boundary prefix. Will be zero or position if the content starts
     // in the current buffer.
     int contentStartIndex;
@@ skipping 255 matching lines @@
   Function partDataReceived;
   Function partEnd;
 }
 
 
 class MimeParserException implements Exception {
   const MimeParserException([String this.message = ""]);
   String toString() => "MimeParserException: $message";
   final String message;
 }