Reapply "Access to imports in the VM's runtime mirrors. Extend test coverage of the source mirrors."

tests/lib/mirrors/library_imports_shown.dart

Index: tests/lib/mirrors/library_imports_shown.dart
diff --git a/tests/language/duplicate_import_prefix_test.dart b/tests/lib/mirrors/library_imports_shown.dart
similarity index 54%
copy from tests/language/duplicate_import_prefix_test.dart
copy to tests/lib/mirrors/library_imports_shown.dart
index 9c288029ab40a7aee66ffeb1f67467e34bdc80fc..6790902e6953b560e6217a51d31154ac1fd25b2c 100644
--- a/tests/language/duplicate_import_prefix_test.dart
+++ b/tests/lib/mirrors/library_imports_shown.dart
@@ -2,9 +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.
 
-// Importing with a duplicate prefix is allowed.
+library library_imports_shown;
 
-import "duplicate_import_liba.dart" as a;
-import "duplicate_import_libb.dart" as a;
+import 'library_imports_a.dart' show somethingFromA, somethingFromBoth;
+import 'library_imports_b.dart' show somethingFromB;
 
-void main() {}
+var somethingFromShown;