Add the HttpBodyHandler files to the dart:io library

tests/standalone/io/http_body_test.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.
 
 import 'dart:io';
 import 'dart:utf';
 
 import 'package:expect/expect.dart';
 
 void testHttpClientResponseBody() {
-  new HttpBodyHandler();
   void test(String mimeType,
             List<int> content,
             dynamic expectedBody,
             String type,
             [bool shouldFail = false]) {
     HttpServer.bind().then((server) {
       server.listen((request) {
         request.listen(
             (_) {},
             onDone: () {
@@ skipping 136 matching lines @@
        "json");
   test("application/json",
        '{ bad json }'.codeUnits,
        null,
        "json",
        true);
 
   test(null, "body".codeUnits, "body".codeUnits, "binary");
 }
 
-
 void main() {
   testHttpClientResponseBody();
   testHttpServerRequestBody();
 }