Remove _HttpUtils from dart:io.

tests/standalone/io/http_headers_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 "package:expect/expect.dart";
 import 'dart:async';
 import 'dart:math';
 import 'dart:collection';
 
 part '../../../sdk/lib/io/common.dart';
 part "../../../sdk/lib/io/io_sink.dart";
 part "../../../sdk/lib/io/http.dart";
+part "../../../sdk/lib/io/http_date.dart";
 part "../../../sdk/lib/io/http_headers.dart";
 part "../../../sdk/lib/io/http_impl.dart";
 part "../../../sdk/lib/io/http_parser.dart";
-part "../../../sdk/lib/io/http_utils.dart";
 part "../../../sdk/lib/io/socket.dart";
 
 void testMultiValue() {
   _HttpHeaders headers = new _HttpHeaders("1.1");
   Expect.isNull(headers[HttpHeaders.PRAGMA]);
   headers.add(HttpHeaders.PRAGMA, "pragma1");
   Expect.equals(1, headers[HttpHeaders.PRAGMA].length);
   Expect.equals(1, headers["pragma"].length);
   Expect.equals(1, headers["Pragma"].length);
   Expect.equals(1, headers["PRAGMA"].length);
@@ skipping 398 matching lines @@
   testIfModifiedSince();
   testHost();
   testEnumeration();
   testHeaderValue();
   testContentType();
   testContentTypeCache();
   testCookie();
   testInvalidCookie();
   testHeaderLists();
 }