First pass at asynchronous input loading in dart2js.

tests/compiler/dart2js/class_codegen_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.
 // Test that parameters keep their names in the output.
 
+import 'dart:async';
 import "package:expect/expect.dart";
 import 'compiler_helper.dart';
 import 'parser_helper.dart';
 
 const String TEST_ONE = r"""
 class A { }
 class B { }
 
 main() {
   new A();
@@ skipping 41 matching lines @@
   var a;
   A(a) : this.a = a {}
 }
 
 main() {
   new A(3);
 }
 """;
 
 twoClasses() {
-  String generated = compileAll(TEST_ONE);
-  Expect.isTrue(generated.contains('A: {"": "Object;"'));
-  Expect.isTrue(generated.contains('B: {"": "Object;"'));
+  return compileAll(TEST_ONE).then((generated) {
+    Expect.isTrue(generated.contains('A: {"": "Object;"'));
+    Expect.isTrue(generated.contains('B: {"": "Object;"'));
+  });
 }
 
 subClass() {
   checkOutput(String generated) {
     Expect.isTrue(generated.contains('A: {"": "Object;"'));
     Expect.isTrue(generated.contains('B: {"": "A;"'));
   }
 
-  checkOutput(compileAll(TEST_TWO));
-  checkOutput(compileAll(TEST_THREE));
+  compileAll(TEST_TWO).then(checkOutput);
+  compileAll(TEST_THREE).then(checkOutput);
 }
 
 fieldTest() {
-  String generated = compileAll(TEST_FOUR);
-  Expect.isTrue(generated.contains(r"""B: {"": "A;y,z,x"}"""));
+  return compileAll(TEST_FOUR).then((generated) {
+    Expect.isTrue(generated.contains(r"""B: {"": "A;y,z,x"}"""));
+  });
 }
 
 constructor1() {
-  String generated = compileAll(TEST_FIVE);
-  Expect.isTrue(generated.contains(new RegExp(r"new [$a-z]+\.A\(a\);")));
+  return compileAll(TEST_FIVE).then((generated) {
+    Expect.isTrue(generated.contains(new RegExp(r"new [$a-z]+\.A\(a\);")));
+  });
 }
 
 main() {
   twoClasses();
   subClass();
   fieldTest();
   constructor1();
 }