Address comments from https://codereview.chromium.org/14690009

pkg/scheduled_test/test/substitute_future_test.dart

Index: pkg/scheduled_test/test/substitute_future_test.dart
diff --git a/pkg/scheduled_test/test/substitute_future_test.dart b/pkg/scheduled_test/test/substitute_future_test.dart
index 5cffb4b6b62ee494a1071529b935ee6d08898573..b3cade8c434c23d8e78b2d2f4d887b59d1df9c60 100644
--- a/pkg/scheduled_test/test/substitute_future_test.dart
+++ b/pkg/scheduled_test/test/substitute_future_test.dart
@@ -148,9 +148,9 @@ void main() {
     var completer = new Completer();
     var future = new SubstituteFuture(completer.future);
     completer.complete('success');
-    future.then(expectAsync1((_) {
-      expect(() => future.substitute(new Future.value()),
-          throwsStateError);
-    }));
+    // The completer finishes asynchronously. So we have to wait for it to
+    // be completed before we can substitute.
+    expect(future.then((_) => future.substitute(new Future.value())),
+        throwsStateError);
   });
 }