Decorate mixin application class name with private keys of libraries of super

tests/language/regress_27957_lib2.dart

Index: tests/language/regress_27957_lib2.dart
diff --git a/tests/language/regress_27957_lib2.dart b/tests/language/regress_27957_lib2.dart
new file mode 100644
index 0000000000000000000000000000000000000000..24097d09f8adc2883327de9a8538c2cc0ea33b1a
--- /dev/null
+++ b/tests/language/regress_27957_lib2.dart
@@ -0,0 +1,9 @@
+// Copyright (c) 2016, 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 file.
+
+library regress_27957_lib2;
+
+class Superclass {
+  int m() => 2;
+}