First pass at asynchronous input loading in dart2js.

tests/compiler/dart2js/simple_inferrer_final_field2_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.
 
 // Test that a non-used generative constructor does not prevent
 // infering types for fields.
 
 import 'package:expect/expect.dart';
+import "package:async_helper/async_helper.dart";
 import 'compiler_helper.dart';
 import 'parser_helper.dart';
 
 const String TEST = """
 
 class A {
   final intField;
   final stringField;
   A() : intField = 42, stringField = 'foo';
   A.bar() : intField = 54, stringField = 42;
 }
 
 main() {
   new A();
 }
 """;
 
 void main() {
   Uri uri = new Uri(scheme: 'source');
   var compiler = compilerFor(TEST, uri);
-  compiler.runCompiler(uri);
-  var typesInferrer = compiler.typesTask.typesInferrer;
+  asyncTest(() => compiler.runCompiler(uri).then((_) {
+    var typesInferrer = compiler.typesTask.typesInferrer;
 
-  checkFieldTypeInClass(String className, String fieldName, type) {
-    var cls = findElement(compiler, className);
-    var element = cls.lookupLocalMember(buildSourceString(fieldName));
-    Expect.equals(type, typesInferrer.getTypeOfElement(element));
-  }
+    checkFieldTypeInClass(String className, String fieldName, type) {
+      var cls = findElement(compiler, className);
+      var element = cls.lookupLocalMember(buildSourceString(fieldName));
+      Expect.equals(type, typesInferrer.getTypeOfElement(element));
+    }
 
-  checkFieldTypeInClass('A', 'intField', compiler.typesTask.intType);
-  checkFieldTypeInClass('A', 'stringField', compiler.typesTask.stringType);
+    checkFieldTypeInClass('A', 'intField', compiler.typesTask.intType);
+    checkFieldTypeInClass('A', 'stringField', compiler.typesTask.stringType);
+  }));
 }