Implement support for application/x-www-form-urlencoded' form data in HttpBodyHandler.

sdk/lib/io/http_multipart_form_data_impl.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.
 
 part of dart.io;
 
 
 class _HttpMultipartFormData extends Stream implements HttpMultipartFormData {
   final ContentType contentType;
   final HeaderValue contentDisposition;
@@ skipping 23 matching lines @@
       StringBuffer buffer = new StringBuffer();
       Encoding encoding;
       if (contentType != null) {
         encoding = Encoding.fromName(contentType.charset);
       }
       if (encoding == null) encoding = Encoding.ISO_8859_1;
       _stream = _stream
           .transform(new StringDecoder(encoding))
           .expand((data) {
             buffer.write(data);
-            var out = _HttpUtils.parseHttpEntityString(buffer.toString());
+            var out = _HttpUtils.decodeHttpEntityString(buffer.toString());
             if (out != null) {
               buffer = new StringBuffer();
               return [out];
             }
             return const [];
           });
     }
   }
 
   bool get isText => _isText;
@@ skipping 38 matching lines @@
                           onDone: onDone,
                           onError: onError,
                           cancelOnError: cancelOnError);
   }
 
   String value(String name) {
     return _mimeMultipart.headers[name];
   }
 }