First pass at asynchronous input loading in dart2js.

tests/compiler/dart2js/simple_inferrer_relations_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
     '../../../sdk/lib/_internal/compiler/implementation/types/types.dart'
     show TypeMask;
 
 import 'compiler_helper.dart';
@@ skipping 33 matching lines @@
   var b = new B(0, inscrutable(0) == 0 ? 2 : "horse");
   var c = inscrutable(0) == 0 ? a : "kurt";
   var d = inscrutable(0) == 0 ? b : "gert";
   if (c == d) {
     print("hestfisk");
   }
 }
 """;
 
 void main() {
-  String generated = compileAll(TEST);
-  if (generated.contains(r'=== true')) {
-    print(generated);
-    Expect.fail("missing elision of '=== true'");
-  }
+  compileAll(TEST).then((generated) {
+    if (generated.contains(r'=== true')) {
+      print(generated);
+      Expect.fail("missing elision of '=== true'");
+    }
+  });
 }