Ensure that failure to start an isolate all end up in the future.

tests/isolate/isolate_create_error_helper_lib4.dart

Index: tests/isolate/isolate_create_error_helper_lib4.dart
diff --git a/pkg/docgen/test/multi_library_code/lib/root_lib.dart b/tests/isolate/isolate_create_error_helper_lib4.dart
similarity index 54%
copy from pkg/docgen/test/multi_library_code/lib/root_lib.dart
copy to tests/isolate/isolate_create_error_helper_lib4.dart
index 74423abfeba22b68b7561d308758df0fdd7d9e60..294e854563f240be1870fc25e8e44e5a8cb000d0 100644
--- a/pkg/docgen/test/multi_library_code/lib/root_lib.dart
+++ b/tests/isolate/isolate_create_error_helper_lib4.dart
@@ -2,12 +2,9 @@
 // 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.
 
-library root_lib;
+library isolate.create.error_helper4_lib;
 
-export 'test_lib.dart';
-export 'test_lib_foo.dart';
-export 'test_lib_bar.dart';
+// This library has a main that is not a function,
+// but does have a function type.
 
-class RootClass {
-  RootClass(int a, int b);
-}
+final main = () { print("Not a function declaration!"); };