Ensure constructorName symbols include private manglings.

runtime/lib/mirrors_impl.dart

Index: runtime/lib/mirrors_impl.dart
diff --git a/runtime/lib/mirrors_impl.dart b/runtime/lib/mirrors_impl.dart
index 85bbae8387d0bdcee6a7ab820692fef7ebdcf681..90f160850f8bd4e59dfbe4db123dc9be288f694c 100644
--- a/runtime/lib/mirrors_impl.dart
+++ b/runtime/lib/mirrors_impl.dart
@@ -1336,7 +1336,8 @@ class _LocalMethodMirrorImpl extends _LocalDeclarationMirrorImpl
               'Internal error in MethodMirror.constructorName: '
               'malformed name <$simpleName>');
         } else if (parts.length == 2) {
-          _constructorName = _s(parts[1]);
+          LibraryMirror definingLibrary = owner.owner;
+          _constructorName = MirrorSystem.getSymbol(parts[1], definingLibrary);
         } else {
           _constructorName = _s('');
         }