commit 4dded7f0bbe1b0eeba9caec805966d6283865241
Author: Jay Callicott <jrcallicott@gmail.com>
Date:   Mon Jun 10 12:47:50 2013 -0500

    Add Attribute namespace

diff --git a/core/includes/theme.maintenance.inc b/core/includes/theme.maintenance.inc
index 79f2b36..cf4466b 100644
--- a/core/includes/theme.maintenance.inc
+++ b/core/includes/theme.maintenance.inc
@@ -6,6 +6,7 @@
  */
 
 use Drupal\Component\Utility\Unicode;
+use Drupal\Core\Template\Attribute;
 
 /**
  * Sets up the theming system for maintenance page.