First pass at asynchronous input loading in dart2js.

tests/compiler/dart2js/string_interpolation_test.dart

Index: tests/compiler/dart2js/string_interpolation_test.dart
diff --git a/tests/compiler/dart2js/string_interpolation_test.dart b/tests/compiler/dart2js/string_interpolation_test.dart
index f6e3bca68df71cce7229b252816779941a90c26a..01ea1bb96e7f1dfc6326dc63e560aaffc10d7d1d 100644
--- a/tests/compiler/dart2js/string_interpolation_test.dart
+++ b/tests/compiler/dart2js/string_interpolation_test.dart
@@ -3,13 +3,17 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import "package:expect/expect.dart";
+import "package:async_helper/async_helper.dart";
 import 'compiler_helper.dart';
 
 main() {
-  String code =
-      compileAll(r'''main() { return "${2}${true}${'a'}${3.14}"; }''');
-  Expect.isTrue(code.contains(r'2truea3.14'));
+  asyncTest(() => compileAll(
+      r'''main() { return "${2}${true}${'a'}${3.14}"; }''').then((code) {
+    Expect.isTrue(code.contains(r'2truea3.14'));
+  }));
 
-  code = compileAll(r'''main() { return "foo ${new Object()}"; }''');
-  Expect.isFalse(code.contains(r'concat'));
+  asyncTest(() => compileAll(
+      r'''main() { return "foo ${new Object()}"; }''').then((code) {
+    Expect.isFalse(code.contains(r'concat'));
+  }));
 }