First pass at asynchronous input loading in dart2js.

tests/compiler/dart2js/no_duplicate_stub_test.dart

 // Copyright (c) 2012, 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 "../../async_helper.dart";
 import 'compiler_helper.dart';
 
 const String TEST = r"""
 class A {
   foo({a, b}) {}
 }
 
 class B extends A {
 }
 
 main() {
   var a = [bar, baz];
   a[0](new A());
   a[1](new A());
 }
 
 bar(a) {
   if (a is A) a.foo(a: 42);
 }
 
 baz(a) {
   if (a is B) a.foo(a: 42);
 }
 """;
 
 main() {
-  String generated = compileAll(TEST);
-  RegExp regexp = new RegExp('foo\\\$1\\\$a: function');
-  Iterator<Match> matches = regexp.allMatches(generated).iterator;
-  checkNumberOfMatches(matches, 1);
+  asyncTest(() => compileAll(TEST).then((generated) {
+    RegExp regexp = new RegExp('foo\\\$1\\\$a: function');
+    Iterator<Match> matches = regexp.allMatches(generated).iterator;
+    checkNumberOfMatches(matches, 1);
+  }));
 }