First pass at asynchronous input loading in dart2js.

tests/compiler/dart2js/inferrer_factory_test.dart

 // Copyright (c) 2013, 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.
 
 import "package:expect/expect.dart";
 import 'compiler_helper.dart';
 
 const String TEST1 = r"""
 class A implements List {
   factory A() {
     // Avoid inlining by using try/catch.
     try {
       return new List();
     } catch (e) {
     }
   }
 }
 
 main() {
   new A()[0] = 42;
 }
 """;
 
 main() {
-  String generated = compileAll(TEST1);
-  // Check that we're using the index operator on the object returned
-  // by the A factory.
-  Expect.isTrue(generated.contains('[0] = 42'));
+  compileAll(TEST1).then((generated) {
+    // Check that we're using the index operator on the object returned
+    // by the A factory.
+    Expect.isTrue(generated.contains('[0] = 42'));
+  });
 }