Address a number of issues related to computation of currentScript and deferred loading.

dart/tests/compiler/dart2js_extra/deferred/deferred_class_test.dart

Index: dart/tests/compiler/dart2js_extra/deferred/deferred_class_test.dart
diff --git a/dart/tests/compiler/dart2js_extra/deferred/deferred_class_test.dart b/dart/tests/compiler/dart2js_extra/deferred/deferred_class_test.dart
index 4eaa40df201dd1938f3dc792c0e005ad52d62797..7e05fbd197bd4d86ba3c4d5ee237540f14fa6d8d 100644
--- a/dart/tests/compiler/dart2js_extra/deferred/deferred_class_test.dart
+++ b/dart/tests/compiler/dart2js_extra/deferred/deferred_class_test.dart
@@ -2,7 +2,10 @@
 // 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.
 
-import "package:expect/expect.dart";
+import '../../../async_helper.dart';
+
+import 'package:expect/expect.dart';
+
 import 'dart:async';
 
 @lazy import 'deferred_class_library.dart';
@@ -16,21 +19,25 @@ main() {
   Expect.throws(() { x = new MyClass(); }, isNoSuchMethodError);
   Expect.isNull(x);
   int counter = 0;
+  asyncStart();
   lazy.load().then((bool didLoad) {
     Expect.isTrue(didLoad);
     Expect.equals(1, ++counter);
     print('deferred_class_library was loaded');
     x = new MyClass();
     Expect.equals(42, x.foo(87));
+    asyncEnd();
   });
   Expect.equals(0, counter);
   Expect.isNull(x);
+  asyncStart();
   lazy.load().then((bool didLoad) {
     Expect.isFalse(didLoad);
     Expect.equals(2, ++counter);
     print('deferred_class_library was loaded');
     x = new MyClass();
     Expect.equals(42, x.foo(87));
+    asyncEnd();
   });
   Expect.equals(0, counter);
   Expect.isNull(x);