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

pkg/http_server/lib/src/http_body.dart

 // Copyright (c) 2013, 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;
 
 
 /**
  * [HttpBodyHandler] is a helper class for processing and collecting
  * HTTP message data in an easy-to-use [HttpBody] object. The content
@@ skipping 85 matching lines @@
 
   /**
    * Create a new [HttpBodyHandler] to be used with a [Stream]<[HttpRequest]>,
    * e.g. a [HttpServer].
    *
    * If the page is served using different encoding than UTF-8, set
    * [defaultEncoding] accordingly. This is required for parsing
    * `multipart/form-data` content correctly. See the class comment
    * for more information on `multipart/form-data`.
    */
-  HttpBodyHandler({Encoding defaultEncoding: Encoding.UTF_8})
+  HttpBodyHandler({Encoding defaultEncoding: UTF8})
       : _transformer = new _HttpBodyHandlerTransformer(defaultEncoding);
 
   /**
    * Process and parse an incoming [HttpRequest]. The returned [HttpRequestBody]
    * contains a [response] field for accessing the [HttpResponse].
    *
    * See [HttpBodyHandler] constructor for more info on [defaultEncoding].
    */
   static Future<HttpRequestBody> processRequest(
       HttpRequest request,
-      {Encoding defaultEncoding: Encoding.UTF_8}) {
+      {Encoding defaultEncoding: UTF8}) {
     return _HttpBodyHandler.processRequest(request, defaultEncoding);
   }
 
   /**
    * Process and parse an incoming [HttpClientResponse].
    *
    * See [HttpBodyHandler] constructor for more info on [defaultEncoding].
    */
   static Future<HttpClientResponseBody> processResponse(
       HttpClientResponse response,
-      {Encoding defaultEncoding: Encoding.UTF_8}) {
+      {Encoding defaultEncoding: UTF8}) {
     return _HttpBodyHandler.processResponse(response, defaultEncoding);
   }
 
   Stream<HttpRequestBody> bind(Stream<HttpRequest> stream) {
     return _transformer.bind(stream);
   }
 }
 
 
 /**
@@ skipping 90 matching lines @@
    * The [ContentType] of the uploaded file. For 'text/\*' and
    * 'application/json' the [data] field will a String.
    */
   ContentType get contentType;
 
   /**
    * The content of the file. Either a [String] or a [List<int>].
    */
   dynamic get content;
 }