Remove Encoding-enum from dart:io and add interface in dart:convert.

pkg/http_server/lib/src/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 http_server;
 
 
 class _HttpMultipartFormData extends Stream implements HttpMultipartFormData {
   final ContentType contentType;
   final HeaderValue contentDisposition;
@@ skipping 16 matching lines @@
                               "${contentTransferEncoding.value}");
     }
 
     if (contentType == null ||
         contentType.primaryType == 'text' ||
         contentType.mimeType == 'application/json') {
       _isText = true;
       StringBuffer buffer = new StringBuffer();
       Encoding encoding;
       if (contentType != null) {
-        encoding = Encoding.fromName(contentType.charset);
+        encoding = Encoding.getByName(contentType.charset);
       }
-      if (encoding == null) encoding = Encoding.ISO_8859_1;
+      if (encoding == null) encoding = LATIN1;
       _stream = _stream
-          .transform(new StringDecoder(encoding))
+          .transform(encoding.decoder)
           .expand((data) {
             buffer.write(data);
             var out = _decodeHttpEntityString(buffer.toString());
             if (out != null) {
               buffer.clear();
               return [out];
             }
             return const [];
           });
     }
@@ skipping 77 matching lines @@
     while ((amp = input.indexOf('&', offset)) >= 0) {
       buffer.write(input.substring(offset, amp));
       int end = input.indexOf(';', amp);
       parse(amp, end);
       offset = end + 1;
     }
     buffer.write(input.substring(offset));
     return buffer.toString();
   }
 }