Added async_helper and fixed broken asynchronous test.

tests/html/indexeddb_2_test.dart

 library IndexedDB1Test;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 import 'dart:async';
 import 'dart:html' as html;
 import 'dart:indexed_db' as idb;
 import 'dart:collection';
 import 'utils.dart';
 
 // Write and re-read Maps: simple Maps; Maps with DAGs; Maps with cycles.
 
 const String DB_NAME = 'Test2';
 const String STORE_NAME = 'TEST';
 const int VERSION = 1;
 
 testReadWrite(key, value, check,
               [dbName = DB_NAME, storeName = STORE_NAME, version = VERSION]) {
 
   createObjectStore(e) {
     var store = e.target.result.createObjectStore(storeName);
     expect(store, isNotNull);
   }
 
   var db;
   // Delete any existing DBs.
-  return html.window.indexedDB.deleteDatabase(dbName).then((_) {
+  return html.window.indexedDB.deleteDatabase(dbName).then(expectAsync1((_) {
       return html.window.indexedDB.open(dbName, version: version,
         onUpgradeNeeded: createObjectStore);
-    }).then((result) {
+    })).then(expectAsync1((result) {
       db = result;
       var transaction = db.transaction([storeName], 'readwrite');
       transaction.objectStore(storeName).put(value, key);
 
       return transaction.completed;
-    }).then((db) {
+    })).then(expectAsync1((db) {
       var transaction = db.transaction(storeName, 'readonly');
       return transaction.objectStore(storeName).getObject(key);
-    }).then((object) {
+    })).then(expectAsync1((object) {
       db.close();
       check(value, object);
-    }).catchError((e) {
+    })).catchError((e) {
       if (db != null) {
         db.close();
       }
       throw e;
     });
 }
 
 List<String> get nonNativeListData {
   var list = new List<String>();
   list.add("data");
@@ skipping 45 matching lines @@
     go('test_cycle', obj3);
     go('test_simple_splay', obj4);
     go('const_array_1', const [const [1], const [2]]);
     go('const_array_dag', const [const [1], const [1]]);
     go('array_deferred_copy', [1,2,3, obj3, obj3, 6]);
     go('array_deferred_copy_2', [1,2,3, [4, 5, obj3], [obj3, 6]]);
     go('cyclic_list', cyclic_list);
     go('non-native lists', nonNativeListData);
   }
 }