First pass at asynchronous input loading in dart2js.

tests/compiler/dart2js/regress_10231_test.dart

Index: tests/compiler/dart2js/regress_10231_test.dart
diff --git a/tests/compiler/dart2js/regress_10231_test.dart b/tests/compiler/dart2js/regress_10231_test.dart
index bc3a36f45452855b7a1052bd246cce57d92ec58b..2e0646139e83cf363d4efff0b77c64c1675c7b6f 100644
--- a/tests/compiler/dart2js/regress_10231_test.dart
+++ b/tests/compiler/dart2js/regress_10231_test.dart
@@ -5,13 +5,16 @@
 // Regression test for http://dartbug.com/10231.
 
 import 'package:expect/expect.dart';
+import "package:async_helper/async_helper.dart";
 import 'codegen_helper.dart';
 
 void main() {
-  var code = generate(SOURCE)['test'];
-  Expect.isNotNull(code);
-  Expect.equals(0, new RegExp('add').allMatches(code).length);
-  Expect.equals(3, new RegExp('\\+').allMatches(code).length);
+  asyncTest(() => generate(SOURCE).then((result) {
+    var code = result['test'];
+    Expect.isNotNull(code);
+    Expect.equals(0, new RegExp('add').allMatches(code).length);
+    Expect.equals(3, new RegExp('\\+').allMatches(code).length);
+  }));
 }
 
 const String SOURCE = """