Restructure outline shaker tests.

pkg/front_end/testcases/shaker/target_top_variable.dart

Index: pkg/front_end/testcases/shaker/target_top_variable.dart
diff --git a/pkg/front_end/testcases/shaker/include_field_type.dart b/pkg/front_end/testcases/shaker/target_top_variable.dart
similarity index 78%
copy from pkg/front_end/testcases/shaker/include_field_type.dart
copy to pkg/front_end/testcases/shaker/target_top_variable.dart
index f7c77d5825a3fe8da66efc1c4d0587a43f278fe0..0818f4cf5718450fe2fde1b774371d7640a7c8bb 100644
--- a/pkg/front_end/testcases/shaker/include_field_type.dart
+++ b/pkg/front_end/testcases/shaker/target_top_variable.dart
@@ -2,6 +2,6 @@
 // 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/targets_top.dart';
 
-foo(F x) => x.field;
+var v = myTopLevelVariable;