Remove _HttpUtils from dart:io.

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() {
@@ skipping 237 matching lines @@
 
   test('application/x-www-form-urlencoded',
        '%E5%B9%B3%3D%E4%BB%AE%E5%90%8D=%E5%B9%B3%E4%BB%AE%E5%90%8D&b'
        '=%E5%B9%B3%E4%BB%AE%E5%90%8D'.codeUnits,
        { 'b' : '平仮名',
          '平=仮名' : '平仮名'},
        "form");
 
   test('application/x-www-form-urlencoded',
        'a=%F8+%26%23548%3B'.codeUnits,
-       { 'a' : '\u{FFFD}Ȥ' },
+       { 'a' : '\u{FFFD} Ȥ' },
        "form");
 
   test('application/x-www-form-urlencoded',
+       'a=%C0%A0'.codeUnits,
+       { 'a' : '\u{FFFD}' },
+       "form");
+
+  test('application/x-www-form-urlencoded',
+       'a=x%A0x'.codeUnits,
+       { 'a' : 'x\u{FFFD}x' },
+       "form");
+
+  test('application/x-www-form-urlencoded',
+       'a=x%C0x'.codeUnits,
+       { 'a' : 'x\u{FFFD}x' },
+       "form");
+
+  test('application/x-www-form-urlencoded',
        'a=%C3%B8+%C8%A4'.codeUnits,
        { 'a' : 'ø Ȥ' },
        "form");
 
   test('application/x-www-form-urlencoded',
        'a=%F8+%26%23548%3B'.codeUnits,
        { 'a' : 'ø Ȥ' },
        "form",
        defaultEncoding: Encoding.ISO_8859_1);
 
@@ skipping 44 matching lines @@
   test('application/x-www-form-urlencoded',
        'name=%C8%A4%C8%A4'.codeUnits,
        { 'name' : 'ȤȤ' },
        "form");
 }
 
 void main() {
   testHttpClientResponseBody();
   testHttpServerRequestBody();
 }