First pass at asynchronous input loading in dart2js.

tests/compiler/dart2js/no_constructor_body_test.dart

Index: tests/compiler/dart2js/no_constructor_body_test.dart
diff --git a/tests/compiler/dart2js/no_constructor_body_test.dart b/tests/compiler/dart2js/no_constructor_body_test.dart
index 0a11b017392d22902ce4f7b7ce7506d9184b5b5f..0a3b388ce1f32e753dfcb9492b54afcbd1f31546 100644
--- a/tests/compiler/dart2js/no_constructor_body_test.dart
+++ b/tests/compiler/dart2js/no_constructor_body_test.dart
@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import "package:expect/expect.dart";
+import "package:async_helper/async_helper.dart";
 import 'compiler_helper.dart';
 
 const String TEST = r"""
@@ -17,7 +18,7 @@ main() {
 """;
 
 main() {
-  String generated = compileAll(TEST);
-  Expect.isTrue(
-      generated.contains('A: {"": "Object;", static:'));
+  asyncTest(() => compileAll(TEST).then((generated) {
+    Expect.isTrue(generated.contains('A: {"": "Object;", static:'));
+  }));
 }