fixes #292, report async_helper test failures

test/codegen/async_helper.dart

Index: test/codegen/async_helper.dart
diff --git a/test/codegen/async_helper.dart b/test/codegen/async_helper.dart
index 37496bcb76bda9156c55f57b6accd2ec6b35895f..be5014fd6efdb7e09e602a8e9a1f62bb3d66bf34 100644
--- a/test/codegen/async_helper.dart
+++ b/test/codegen/async_helper.dart
@@ -23,20 +23,29 @@
 
 library async_helper;
 
-// TODO(kustermann): This is problematic because we rely on a working
-// 'dart:isolate' (i.e. it is in particular problematic with dart2js).
-// It would be nice if we could use a different mechanism for different
-// runtimes.
-import 'dart:isolate';
-
 bool _initialized = false;
-ReceivePort _port = null;
+
+typedef void _Action0();
+_Action0 _onAsyncEnd;
+
 int _asyncLevel = 0;
 
 Exception _buildException(String msg) {
   return new Exception('Fatal: $msg. This is most likely a bug in your test.');
 }
 
+/// Implementation method called from language_tests.js.
+/// Registers the callback that will be used complete the test.
+void asyncTestInitialize(_Action0 callback) {
+  _asyncLevel = 0;
+  _initialized = false;
+  _onAsyncEnd = callback;
+}
+
+/// Implementation method called from language_tests.js.
+/// Returns true if an asyncTest was started.
+bool get asyncTestStarted => _initialized;
+
 /// Call this method before an asynchronous test is created.
 void asyncStart() {
   if (_initialized && _asyncLevel == 0) {
@@ -44,9 +53,14 @@ void asyncStart() {
                           'with testing.');
   }
   if (!_initialized) {
+    if (_onAsyncEnd == null) {
+      throw _buildException(
+          'asyncStart() was called before asyncTestInitialize()');
+    }
+
     print('unittest-suite-wait-for-done');
     _initialized = true;
-    _port = new ReceivePort();
+
   }
   _asyncLevel++;
 }
@@ -63,8 +77,9 @@ void asyncEnd() {
   }
   _asyncLevel--;
   if (_asyncLevel == 0) {
-    _port.close();
-    _port = null;
+    var callback = _onAsyncEnd;
+    _onAsyncEnd = null;
+    callback();
     print('unittest-suite-success');
   }
 }