Add language tests for Issue 18628.

tools/test.dart

 #!/usr/bin/env 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.
 
 /**
  * This file is the entrypoint of the dart test suite.  This suite is used
  * to test:
  *
  *     1. the dart vm
  *     2. the dart2js compiler
  *     3. the static analyzer
  *     4. the dart core library
  *     5. other standard dart libraries (DOM bindings, ui libraries,
  *            io libraries etc.)
  *
  * This script is normally invoked by test.py.  (test.py finds the dart vm
  * and passses along all command line arguments to this script.)
  *
  * The command line args of this script are documented in
- * "tools/testing/test_options.dart".
+ * "tools/testing/dart/test_options.dart"; they are printed
+ * when this script is run with "--help".
  *
+ * The default test directory layout is documented in
+ * "tools/testing/dart/test_suite.dart", above
+ * "factory StandardTestSuite.forDirectory".
  */
 
 library test;
 
 import "dart:async";
 import "dart:io";
 import "dart:math" as math;
 import "testing/dart/browser_controller.dart";
 import "testing/dart/http_server.dart";
 import "testing/dart/test_options.dart";
@@ skipping 278 matching lines @@
   TestUtils.setDartDirUri(Platform.script.resolve('..'));
   deleteTemporaryDartDirectories().then((_) {
     var optionsParser = new TestOptionsParser();
     var configurations = optionsParser.parse(arguments);
     if (configurations != null && configurations.length > 0) {
       testConfigurations(configurations);
     }
   });
 }