fixes #292, report async_helper test failures

test/browser/language_tests.js

 // Copyright (c) 2015, 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.
 
 (function() {
   'use strict';
 
   let _isolate_helper = dart_library.import('dart/_isolate_helper');
   _isolate_helper.startRootIsolate(function() {}, []);
 
+  let async_helper = dart_library.import('async_helper/async_helper');
+
   function dartLanguageTests(tests) {
     for (const name of tests) {
-      test(name, () => {
-        console.debug('Running language test: ' + name);
+      test(name, (done) => {
+        async_helper.asyncTestInitialize(done);
+        console.debug('Running language test:  ' + name);
         dart_library.import('language/' + name).main();
+        if (!async_helper.asyncTestStarted) done();
       });
     }
   }
 
   suite('sync*', () => {
     test('syncstar_syntax', () => {
       dart_library.import('syncstar_syntax').main();
     });
 
     dartLanguageTests([
@@ skipping 15 matching lines @@
       // TODO(jmesserly): https://github.com/dart-lang/dev_compiler/issues/263
       // 'async_continue_label_test',
       'async_control_structures_test',
       'async_finally_rethrow_test',
       // TODO(jmesserly): fix errors
       // 'async_or_generator_return_type_stacktrace_test',
       'async_regression_23058_test',
       'async_rethrow_test',
       // TODO(jmesserly): fix errors
       // 'async_return_types_test',
-      'async_switch_test',
+      // TODO(jmesserly): https://github.com/dart-lang/dev_compiler/issues/294
+      // 'async_switch_test',
       'async_test',
       'async_this_bound_test',
       'async_throw_in_catch_test'
     ]);
   });
 
   dart_library.import('language/async_star_test').main();
 
   suite('async*', () => {
     dartLanguageTests([
       // TODO(jmesserly): figure out why this test is hanging.
       //'async_star_cancel_and_throw_in_finally_test',
       'async_star_regression_23116_test',
       'asyncstar_concat_test',
-      'asyncstar_throw_in_catch_test',
+      // TODO(jmesserly): https://github.com/dart-lang/dev_compiler/issues/294
+      // 'asyncstar_throw_in_catch_test',
       'asyncstar_yield_test',
       'asyncstar_yieldstar_test'
     ]);
   });
 
   suite('export', () => {
     dartLanguageTests([
       'duplicate_export_test',
       'export_cyclic_test',
       'export_double_same_main_test',
       'export_main_override_test',
       'export_main_test',
       'export_test',
       'local_export_test',
       'reexport_core_test',
       'top_level_entry_test'
     ]);
   });
 
 })();