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

tests/isolate/isolate_create_error_helper_lib2.dart

Index: tests/isolate/isolate_create_error_helper_lib2.dart
diff --git a/pkg/docgen/test/multi_library_code/lib/root_lib.dart b/tests/isolate/isolate_create_error_helper_lib2.dart
similarity index 54%
copy from pkg/docgen/test/multi_library_code/lib/root_lib.dart
copy to tests/isolate/isolate_create_error_helper_lib2.dart
index 74423abfeba22b68b7561d308758df0fdd7d9e60..b34983348f93e39beed15cfb975859346ce5ad02 100644
--- a/pkg/docgen/test/multi_library_code/lib/root_lib.dart
+++ b/tests/isolate/isolate_create_error_helper_lib2.dart
@@ -2,12 +2,10 @@
 // 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_helper2_lib;
 
-export 'test_lib.dart';
-export 'test_lib_foo.dart';
-export 'test_lib_bar.dart';
+// This library has a main method with wrong parameters.
 
-class RootClass {
-  RootClass(int a, int b);
+void main(a, b, c) {
+  print("Three required positional parameters: $a, $b, $c");
 }