Add mirrors tests

test/codegen/lib/mirrors/library_imports_b.dart

Index: test/codegen/lib/mirrors/library_imports_b.dart
diff --git a/test/codegen/language/deferred_shadow_load_library_lib.dart b/test/codegen/lib/mirrors/library_imports_b.dart
similarity index 75%
copy from test/codegen/language/deferred_shadow_load_library_lib.dart
copy to test/codegen/lib/mirrors/library_imports_b.dart
index e7811aaaf594ef108f931399a08ecb93761ccfdf..493f3239ae4211b96bcaa19ddfa87513ad8b8d16 100644
--- a/test/codegen/language/deferred_shadow_load_library_lib.dart
+++ b/test/codegen/lib/mirrors/library_imports_b.dart
@@ -2,6 +2,7 @@
 // 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.
 
-loadLibrary() => 42;
+library library_imports_b;
 
-var trueVar = true;
+var somethingFromB;
+var somethingFromBoth;