Reapply "Fix URI encoding/decoding of + and space""

tests/standalone/io/url_encoding_test.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.
 
 import "dart:utf";
 part "../../../sdk/lib/io/input_stream.dart";
 part "../../../sdk/lib/io/output_stream.dart";
 part "../../../sdk/lib/io/chunked_stream.dart";
 part "../../../sdk/lib/io/string_stream.dart";
 part "../../../sdk/lib/io/stream_util.dart";
 part "../../../sdk/lib/io/http.dart";
 part "../../../sdk/lib/io/http_impl.dart";
 part "../../../sdk/lib/io/http_parser.dart";
 part "../../../sdk/lib/io/http_utils.dart";
 
 void testParseEncodedString() {
   String encodedString = 'foo+bar%20foobar%25%26';
   Expect.equals(_HttpUtils.decodeUrlEncodedString(encodedString),
                 'foo bar foobar%&');
+  encodedString = 'A+%2B+B';
+  Expect.equals(_HttpUtils.decodeUrlEncodedString(encodedString),
+                'A + B');
 }
 
 void testParseQueryString() {
   // The query string includes escaped "?"s, "&"s, "%"s and "="s.
   // These should not affect the splitting of the string.
   String queryString =
       '%3F=%3D&foo=bar&%26=%25&sqrt2=%E2%88%9A2&name=Franti%C5%A1ek';
   Map<String, String> map = _HttpUtils.splitQueryString(queryString);
   for (String key in map.keys) {
     Expect.equals(map[key], { '&'     : '%',
                               'foo'   : 'bar',
                               '?'     : '=',
                               'sqrt2' : '\u221A2',
                               'name'  : 'Franti\u0161ek'}[key]);
   }
   Expect.setEquals(map.keys, ['&', '?', 'foo', 'sqrt2', 'name']);
 }
 
 void main() {
   testParseEncodedString();
   testParseQueryString();
 }