First pass at asynchronous input loading in dart2js.

tests/compiler/dart2js/no_constructor_body_test.dart

Index: tests/compiler/dart2js/no_constructor_body_test.dart
diff --git a/tests/compiler/dart2js/no_constructor_body_test.dart b/tests/compiler/dart2js/no_constructor_body_test.dart
index 666afeb8f31b698b33d4a7b6bbb453701a3730bb..ccec575eab3d152482178a8c0c61f4439da7452a 100644
--- a/tests/compiler/dart2js/no_constructor_body_test.dart
+++ b/tests/compiler/dart2js/no_constructor_body_test.dart
@@ -17,7 +17,7 @@ main() {
 """;
 
 main() {
-  String generated = compileAll(TEST);
-  Expect.isTrue(
-      generated.contains('A: {"": "Object;"}'));
+  compileAll(TEST).then((generated) {
+    Expect.isTrue(generated.contains('A: {"": "Object;"}'));
+  });
 }