Add mirrors tests

test/codegen/lib/mirrors/repeated_private_anon_mixin_app2.dart

Index: test/codegen/lib/mirrors/repeated_private_anon_mixin_app2.dart
diff --git a/test/codegen/language/missing_part_of_tag_test.dart b/test/codegen/lib/mirrors/repeated_private_anon_mixin_app2.dart
similarity index 66%
copy from test/codegen/language/missing_part_of_tag_test.dart
copy to test/codegen/lib/mirrors/repeated_private_anon_mixin_app2.dart
index ffb360cd14801fd0cd4f29ac47107903fd84a480..54259201ef7e6924750a0b240eddf110e4627d64 100644
--- a/test/codegen/language/missing_part_of_tag_test.dart
+++ b/test/codegen/lib/mirrors/repeated_private_anon_mixin_app2.dart
@@ -2,10 +2,10 @@
 // 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.
 
-// Test for missing part-of tag.
-
 library lib;
 
-part 'missing_part_of_tag_part.dart'; /// 01: compile-time error
-
-void main() {}
+class _S {}
+class _M {}
+class _M2 {}
+class MA extends _S with _M {}
+class MA2 extends _S with _M, _M2 {}