commit 9862a6e1db1421768c2bbce9bc1449bf12581600
Author: Sally Young <sally@justafish.co.uk>
Date:   Wed Nov 14 16:00:06 2012 -0500

    Convert admin_compact_mode to CMI

diff --git a/core/modules/system/config/system.site.yml b/core/modules/system/config/system.site.yml
index 010dedf..ee9b6a7 100644
--- a/core/modules/system/config/system.site.yml
+++ b/core/modules/system/config/system.site.yml
@@ -5,3 +5,4 @@ page:
   403: ''
   404: ''
   front: user
+admin_compact_mode: '0'
diff --git a/core/modules/system/system.install b/core/modules/system/system.install
index e29674e..ac5584f 100644
--- a/core/modules/system/system.install
+++ b/core/modules/system/system.install
@@ -2224,6 +2224,17 @@ function system_update_8035() {
 }
 
 /**
+ * Move the admin_compact_mode setting from variable to config.
+ *
+ * @ingroup config_upgrade
+ */
+function system_update_8036() {
+  update_variables_to_config('system.site', array(
+    'admin_compact_mode' => 'admin_compact_mode',
+  ));
+}
+
+/**
  * @} End of "defgroup updates-7.x-to-8.x".
  * The next series of updates should start at 9000.
  */
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index 843ed78..16b1257 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -3399,7 +3399,7 @@ function confirm_form($form, $question, $path, $description = NULL, $yes = NULL,
 function system_admin_compact_mode() {
   // PHP converts dots into underscores in cookie names to avoid problems with
   // its parser, so we use a converted cookie name.
-  return isset($_COOKIE['Drupal_visitor_admin_compact_mode']) ? $_COOKIE['Drupal_visitor_admin_compact_mode'] : variable_get('admin_compact_mode', FALSE);
+  return isset($_COOKIE['Drupal_visitor_admin_compact_mode']) ? $_COOKIE['Drupal_visitor_admin_compact_mode'] : config('system.site')->get('admin_compact_mode');
 }
 
 /**