Re-land "Search for main in the exported names of the main library, not in the library itself."

tests/language/export_ambiguous_main_a.dart

Index: tests/language/export_ambiguous_main_a.dart
diff --git a/tests/language/regress_13462_0_test.dart b/tests/language/export_ambiguous_main_a.dart
similarity index 76%
copy from tests/language/regress_13462_0_test.dart
copy to tests/language/export_ambiguous_main_a.dart
index b87bf1f24d7378ea99edd41562464cc8f67ffed6..4a7b820ac658b7a8fa19066d6e4302e69289aa7c 100644
--- a/tests/language/regress_13462_0_test.dart
+++ b/tests/language/export_ambiguous_main_a.dart
@@ -2,8 +2,8 @@
 // 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 'dart:mirrors';
+library export_ambiguous_main_a;
 
 main() {
-  print(MirrorSystem.getName(#foo));
+  print('export_ambiguous_main_a');
 }