Restructure outline shaker tests.

pkg/front_end/testcases/shaker/target_top_class.dart

Index: pkg/front_end/testcases/shaker/target_top_class.dart
diff --git a/pkg/front_end/testcases/shaker/include_field_type.dart b/pkg/front_end/testcases/shaker/target_top_class.dart
similarity index 83%
copy from pkg/front_end/testcases/shaker/include_field_type.dart
copy to pkg/front_end/testcases/shaker/target_top_class.dart
index f7c77d5825a3fe8da66efc1c4d0587a43f278fe0..893d9ef51972b3f67bfad5618fd49a2cf4b19490 100644
--- a/pkg/front_end/testcases/shaker/include_field_type.dart
+++ b/pkg/front_end/testcases/shaker/target_top_class.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;
+MyClass c;