First step for modular output in fasta.

pkg/front_end/testcases/shaker/transitive_mixins.dart

Index: pkg/front_end/testcases/shaker/transitive_mixins.dart
diff --git a/pkg/front_end/testcases/shaker/transitive_mixins.dart b/pkg/front_end/testcases/shaker/transitive_mixins.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';
+
+/// We pull in transitive super types from mixins and interfaces.
+foo(M1 x) => null;