First step for modular output 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
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index 0000000000000000000000000000000000000000..7266147217a5eecd96c2b970a31962cd327021d6
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+++ b/pkg/front_end/testcases/shaker/transitive_superclass.dart
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+// 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();