First pass at asynchronous input loading in dart2js.

tests/compiler/dart2js/analyze_dart2js_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.
 
 library analyze_api;
 
 import "package:expect/expect.dart";
 import '../../../sdk/lib/_internal/compiler/implementation/filenames.dart';
 import 'analyze_helper.dart';
+import "package:async_helper/async_helper.dart";
 
 /**
  * Map of whitelisted warnings and errors.
  *
  * Only add a whitelisting together with a bug report to dartbug.com and add
  * the bug issue number as a comment on the whitelisting.
  *
  * Use an identifiable suffix of the file uri as key. Use a fixed substring of
  * the error/warning message in the list of whitelistings for each file.
  */
 // TODO(johnniwinther): Support canonical URIs as keys and message kinds as
 // values.
 const Map<String,List<String>> WHITE_LIST = const {
 };
 
 void main() {
   var uri = currentDirectory.resolve(
       'sdk/lib/_internal/compiler/implementation/dart2js.dart');
-  analyze([uri], WHITE_LIST);
+  asyncTest(() => analyze([uri], WHITE_LIST));
 }