Add mirrors tests

test/codegen/lib/mirrors/library_imports_hidden.dart

Index: test/codegen/lib/mirrors/library_imports_hidden.dart
diff --git a/test/codegen/language/cha_deopt1_deferred_lib.dart b/test/codegen/lib/mirrors/library_imports_hidden.dart
similarity index 54%
copy from test/codegen/language/cha_deopt1_deferred_lib.dart
copy to test/codegen/lib/mirrors/library_imports_hidden.dart
index fc0731568cc3de0060136578168eb59ef568299e..deccc64ad16c3d3f4b06b62231c2989630bf0cbd 100644
--- a/test/codegen/language/cha_deopt1_deferred_lib.dart
+++ b/test/codegen/lib/mirrors/library_imports_hidden.dart
@@ -2,12 +2,9 @@
 // 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.
 
-import "cha_deopt1_lib.dart";
+library library_imports_hidden;
 
-class U extends T {
+import 'library_imports_a.dart' hide somethingFromA, somethingFromBoth;
+import 'library_imports_b.dart' hide somethingFromB;
 
-  m() => "good horse";
-
-}
-
-make_u() => new U();
+var somethingFromHidden;