Add language tests for Issue 18628.

tools/testing/dart/test_options.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.
 
 library test_options_parser;
 
 import "dart:io";
 import "drt_updater.dart";
 import "test_suite.dart";
 import "compiler_configuration.dart" show CompilerConfiguration;
@@ skipping 799 matching lines @@
       result.addAll(_expandConfigurations(newConfiguration));
     }
     return result;
   }
 
 
   /**
    * Print out usage information.
    */
   void _printHelp() {
-    print('usage: dart test.dart [options]\n');
+    print('usage: dart test.dart [options] [selector]');
+    print('');
+    print('The optional selector limits the tests that will be run.');
+    print('For example, the selector "language/issue", or equivalently');
+    print('"language/*issue*", limits to test files matching the regexp');
+    print('".*issue.*\\.dart" in the "tests/language" directory.');
+    print('');
     print('Options:\n');
     for (var option in _options) {
       print('${option.name}: ${option.description}.');
       for (var name in option.keys) {
         assert(name.startsWith('-'));
         var buffer = new StringBuffer();;
         buffer.write(name);
         if (option.type == 'bool') {
           assert(option.values.isEmpty);
         } else {
@@ skipping 29 matching lines @@
         return option;
       }
     }
     print('Unknown test option $name');
     exit(1);
   }
 
 
   List<_TestOptionSpecification> _options;
 }