Reapply CL: first step for modular support in fasta

pkg/front_end/testcases/shaker/transitive_superclass.dart

Index: pkg/front_end/testcases/shaker/transitive_superclass.dart
diff --git a/pkg/front_end/testcases/shaker/transitive_superclass.dart b/pkg/front_end/testcases/shaker/transitive_superclass.dart
new file mode 100644
index 0000000000000000000000000000000000000000..7266147217a5eecd96c2b970a31962cd327021d6
--- /dev/null
+++ b/pkg/front_end/testcases/shaker/transitive_superclass.dart
@@ -0,0 +1,8 @@
+// Copyright (c) 2017, the Dart project authors. Please see the AUTHORS file
+// 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';
+
+/// B and it's superclass _A should be preserved.
+main() => new B();