Restructure outline shaker tests.

pkg/front_end/testcases/shaker/source_local.dart

Index: pkg/front_end/testcases/shaker/source_local.dart
diff --git a/pkg/front_end/testcases/shaker/toplevel_reference.dart b/pkg/front_end/testcases/shaker/source_local.dart
similarity index 67%
rename from pkg/front_end/testcases/shaker/toplevel_reference.dart
rename to pkg/front_end/testcases/shaker/source_local.dart
index 12f211121509fa9d4dfd401bfe899dbd5e2ebe2f..2537acfa5c1549882cda1dc6f63b13c21d735a0c 100644
--- a/pkg/front_end/testcases/shaker/toplevel_reference.dart
+++ b/pkg/front_end/testcases/shaker/source_local.dart
@@ -2,7 +2,11 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
-import 'lib/lib.dart';
+import 'lib/sources.dart';
 
-/// Direct references to toplevel members are preserved
-main() => toplevel();
+void topLevelFunction() {
+  A1 v1;
+  var v2 = A2;
+  print(v1);
+  print(v2);
+}