diff --git a/core/includes/install.inc b/core/includes/install.inc
index db92987..42ec9ac 100644
--- a/core/includes/install.inc
+++ b/core/includes/install.inc
@@ -425,7 +425,6 @@ function drupal_install_system() {
 
   // Clear out module list and hook implementation statics.
   system_list_reset();
-  module_list_reset();
   module_implements_reset();
 
   config_install_default_config('module', 'system');
diff --git a/core/includes/menu.inc b/core/includes/menu.inc
index 112e4f5..0091f03 100644
--- a/core/includes/menu.inc
+++ b/core/includes/menu.inc
@@ -1623,6 +1623,9 @@ function theme_menu_link(array $variables) {
  */
 function theme_menu_local_task($variables) {
   $link = $variables['element']['#link'];
+  $link += array(
+    'localized_options' => array(),
+  );
   $link_text = $link['title'];
 
   if (!empty($variables['element']['#active'])) {
@@ -1869,8 +1872,8 @@ function menu_local_tasks($level = 0) {
   $data = &drupal_static(__FUNCTION__);
   $root_path = &drupal_static(__FUNCTION__ . ':root_path', '');
   $empty = array(
-    'tabs' => array('count' => 0, 'output' => array()),
-    'actions' => array('count' => 0, 'output' => array()),
+    'tabs' => array(),
+    'actions' => array(),
     'root_path' => &$root_path,
   );
 
@@ -1922,8 +1925,7 @@ function menu_local_tasks($level = 0) {
     // Tab parenting may skip levels, so the number of parts in the path may not
     // equal the depth. Thus we use the $depth counter (offset by 1000 for ksort).
     $depth = 1001;
-    $actions['count'] = 0;
-    $actions['output'] = array();
+    $actions = array();
     while (isset($children[$path])) {
       $tabs_current = array();
       $actions_current = array();
@@ -1960,6 +1962,7 @@ function menu_local_tasks($level = 0) {
               '#theme' => 'menu_local_task',
               '#link' => $link,
               '#active' => TRUE,
+              '#weight' => isset($link['weight']) ? $link['weight'] : NULL,
             );
             $next_path = $item['path'];
             $tab_count++;
@@ -1972,6 +1975,7 @@ function menu_local_tasks($level = 0) {
               $actions_current[] = array(
                 '#theme' => 'menu_local_action',
                 '#link' => $link,
+                '#weight' => isset($link['weight']) ? $link['weight'] : NULL,
               );
               $action_count++;
             }
@@ -1980,6 +1984,7 @@ function menu_local_tasks($level = 0) {
               $tabs_current[] = array(
                 '#theme' => 'menu_local_task',
                 '#link' => $link,
+                '#weight' => isset($link['weight']) ? $link['weight'] : NULL,
               );
               $tab_count++;
             }
@@ -1987,10 +1992,8 @@ function menu_local_tasks($level = 0) {
         }
       }
       $path = $next_path;
-      $tabs[$depth]['count'] = $tab_count;
-      $tabs[$depth]['output'] = $tabs_current;
-      $actions['count'] += $action_count;
-      $actions['output'] = array_merge($actions['output'], $actions_current);
+      $tabs[$depth] = $tabs_current;
+      $actions = array_merge($actions, $actions_current);
       $depth++;
     }
     $data['actions'] = $actions;
@@ -2036,6 +2039,7 @@ function menu_local_tasks($level = 0) {
               '#theme' => 'menu_local_task',
               '#link' => $link,
               '#active' => TRUE,
+              '#weight' => isset($link['weight']) ? $link['weight'] : NULL,
             );
             $next_path = $item['tab_parent'];
             if (isset($tasks[$next_path])) {
@@ -2046,14 +2050,14 @@ function menu_local_tasks($level = 0) {
             $tabs_current[] = array(
               '#theme' => 'menu_local_task',
               '#link' => $link,
+              '#weight' => isset($link['weight']) ? $link['weight'] : NULL,
             );
           }
         }
       }
       $path = $next_path;
       $parent = $next_parent;
-      $tabs[$depth]['count'] = $count;
-      $tabs[$depth]['output'] = $tabs_current;
+      $tabs[$depth] = $tabs_current;
       $depth--;
     }
     // Sort by depth.
@@ -2075,7 +2079,7 @@ function menu_local_tasks($level = 0) {
   }
   // @todo If there are no tabs, then there still can be actions; for example,
   //   when added via hook_menu_local_tasks_alter().
-  elseif (!empty($data['actions']['output'])) {
+  elseif (!empty($data['actions'])) {
     return array('actions' => $data['actions']) + $empty;
   }
   return $empty;
@@ -2188,7 +2192,7 @@ function menu_contextual_links($module, $parent_path, $args) {
 function menu_primary_local_tasks() {
   $links = menu_local_tasks(0);
   // Do not display single tabs.
-  return ($links['tabs']['count'] > 1 ? $links['tabs']['output'] : '');
+  return count($links['tabs']) > 1 ? $links['tabs'] : '';
 }
 
 /**
@@ -2197,7 +2201,7 @@ function menu_primary_local_tasks() {
 function menu_secondary_local_tasks() {
   $links = menu_local_tasks(1);
   // Do not display single tabs.
-  return ($links['tabs']['count'] > 1 ? $links['tabs']['output'] : '');
+  return count($links['tabs']) > 1 ? $links['tabs'] : '';
 }
 
 /**
@@ -2205,7 +2209,7 @@ function menu_secondary_local_tasks() {
  */
 function menu_local_actions() {
   $links = menu_local_tasks();
-  return $links['actions']['output'];
+  return $links['actions'];
 }
 
 /**
@@ -3547,7 +3551,6 @@ function _menu_router_build($callbacks) {
     $item['to_arg_functions'] = empty($to_arg_functions) ? '' : serialize($to_arg_functions);
     $item += array(
       'title' => '',
-      'weight' => 0,
       'type' => MENU_NORMAL_ITEM,
       'module' => '',
       '_number_parts' => $number_parts,
@@ -3555,6 +3558,9 @@ function _menu_router_build($callbacks) {
       '_fit' => $fit,
     );
     $item += array(
+      // Default MENU_DEFAULT_LOCAL_TASKs to a weight of -10, so they appear as
+      // first tab by default.
+      'weight' => ($item['type'] & MENU_DEFAULT_LOCAL_TASK) == MENU_DEFAULT_LOCAL_TASK ? -10 : 0,
       '_visible' => (bool) ($item['type'] & MENU_VISIBLE_IN_BREADCRUMB),
       '_tab' => (bool) ($item['type'] & MENU_IS_LOCAL_TASK),
     );
diff --git a/core/includes/module.inc b/core/includes/module.inc
index c1d99f2..285cdf2 100644
--- a/core/includes/module.inc
+++ b/core/includes/module.inc
@@ -34,7 +34,7 @@ function module_load_all($bootstrap = FALSE, $reset = FALSE) {
 
   // Unless $boostrap is NULL, load the requested set of modules.
   if (isset($bootstrap) && !$has_run) {
-    $type = $bootstrap ? 'bootstrap' : 'module_enabled';
+    $type = $bootstrap ? 'bootstrap' : 'module';
     foreach (module_list($type) as $module) {
       drupal_load('module', $module);
     }
@@ -57,7 +57,7 @@ function module_load_all($bootstrap = FALSE, $reset = FALSE) {
  *
  * @param string $type
  *   The type of list to return:
- *   - module_enabled: All enabled modules.
+ *   - module: All enabled modules.
  *   - bootstrap: All enabled modules required for bootstrap.
  * @param array $fixed_list
  *   (optional) An array of module names to override the list of modules. This
@@ -73,7 +73,7 @@ function module_load_all($bootstrap = FALSE, $reset = FALSE) {
  *
  * @see module_list_reset()
  */
-function module_list($type = 'module_enabled', array $fixed_list = NULL, $reset = FALSE) {
+function module_list($type = 'module', array $fixed_list = NULL, $reset = FALSE) {
   // This static is only used for $fixed_list. It must not be a drupal_static(),
   // since any call to drupal_static_reset() in unit tests would cause an
   // attempt to retrieve the list of modules from the database (which does not
@@ -120,13 +120,13 @@ function module_list_reset() {
  *
  * @param $type
  *   The type of list to return:
- *   - module_enabled: All enabled modules.
+ *   - module: All enabled modules.
  *   - bootstrap: All enabled modules required for bootstrap.
- *   - theme: All themes.
+ *   - theme: All enabled themes.
  *
  * @return
  *   An associative array of modules or themes, keyed by name. For $type
- *   'bootstrap' and 'module_enabled', the array values equal the keys.
+ *   'bootstrap' and 'module', the array values equal the keys.
  *   For $type 'theme', the array values are objects representing the
  *   respective database row, with the 'info' property already unserialized.
  *
@@ -167,13 +167,13 @@ function system_list($type) {
     $lists['bootstrap'] = array_keys($bootstrap_list);
   }
   // Otherwise build the list for enabled modules and themes.
-  elseif (!isset($lists['module_enabled'])) {
+  elseif (!isset($lists['module'])) {
     if ($cached = cache('bootstrap')->get('system_list')) {
       $lists = $cached->data;
     }
-    else {
+    if (!isset($lists[$type])) {
       $lists = array(
-        'module_enabled' => array(),
+        'module' => array(),
         'theme' => array(),
         'filepaths' => array(),
       );
@@ -182,11 +182,11 @@ function system_list($type) {
       // Drupal installations, which might have modules installed in different
       // locations in the file system. The ordering here must also be
       // consistent with the one used in module_implements().
-      $enabled_modules = config('system.module')->get('enabled');
+      $enabled_modules = (array) config('system.module')->get('enabled');
       $module_files = state()->get('system.module.files');
       foreach ($enabled_modules as $name => $weight) {
         // Build a list of all enabled modules.
-        $lists['module_enabled'][$name] = $name;
+        $lists['module'][$name] = $name;
         // Build a list of filenames so drupal_get_filename can use it.
         $lists['filepaths'][] = array(
           'type' => 'module',
@@ -196,31 +196,27 @@ function system_list($type) {
       }
 
       // Build a list of themes.
-      $enabled_themes = config('system.theme')->get('enabled');
-      // @todo Themes include all themes, including disabled/uninstalled. This
-      //   system.theme.data state will go away entirely as soon as themes have
-      //   a proper installation status.
-      // @see http://drupal.org/node/1067408
-      $theme_data = state()->get('system.theme.data');
+      $enabled_themes = (array) config('system.theme')->get('enabled');
+      array_walk($enabled_themes, function (&$value, $key) {
+        $value = 'system.theme.data.' . $key;
+      });
+      $theme_data = (array) state()->getMultiple($enabled_themes);
+      // @todo Remove me?
       if (empty($theme_data)) {
-        // @todo: system_list() may be called from _drupal_bootstrap_code() and
+        // system_list() may be called from _drupal_bootstrap_code() and
         // module_load_all(), in which case system.module is not loaded yet.
         // Prevent a filesystem scan in drupal_load() and include it directly.
-        // @see http://drupal.org/node/1067408
         require_once DRUPAL_ROOT . '/core/modules/system/system.module';
         $theme_data = system_rebuild_theme_data();
       }
       foreach ($theme_data as $name => $theme) {
-        $theme->status = (int) isset($enabled_themes[$name]);
         $lists['theme'][$name] = $theme;
         // Build a list of filenames so drupal_get_filename can use it.
-        if (isset($enabled_themes[$name])) {
-          $lists['filepaths'][] = array(
-            'type' => 'theme',
-            'name' => $name,
-            'filepath' => $theme->filename,
-          );
-        }
+        $lists['filepaths'][] = array(
+          'type' => 'theme',
+          'name' => $name,
+          'filepath' => $theme->filename,
+        );
       }
       // @todo Move into list_themes(). Read info for a particular requested
       //   theme from state instead.
@@ -268,6 +264,7 @@ function system_list($type) {
 function system_list_reset() {
   drupal_static_reset('system_list');
   drupal_static_reset('system_rebuild_module_data');
+  drupal_static_reset('system_rebuild_theme_data');
   drupal_static_reset('list_themes');
   cache('bootstrap')->deleteMultiple(array('bootstrap_modules', 'system_list'));
   cache()->delete('system_info');
diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index 3c4576a..5da4494 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -55,14 +55,44 @@
  */
 
 /**
+ * Loads a theme.
+ *
+ * @param string $name
+ *   The name of a theme to load.
+ *
+ * @return
+ *   The loaded theme object for $name, or FALSE if the passed $name does not
+ *   exist or is not enabled.
+ */
+function theme_load($name) {
+  $themes = list_themes();
+  if (isset($themes[$name]) && drupal_theme_access($themes[$name])) {
+    return $themes[$name];
+  }
+  return FALSE;
+}
+
+/**
+ * Menu title callback; Returns the sanitized human-readable name of a theme.
+ *
+ * @param $theme
+ *   The theme object to return the title for.
+ *
+ * This needs to be a private function to avoid clashing with a possible
+ * theme_menu_title() theme function by Menu or a potential Menu Title module.
+ */
+function _theme_menu_title($theme) {
+  return check_plain($theme->info['name']);
+}
+
+/**
  * Determines if a theme is available to use.
  *
  * @param $theme
  *   Either the name of a theme or a full theme object.
  *
  * @return
- *   Boolean TRUE if the theme is enabled or is the site administration theme;
- *   FALSE otherwise.
+ *   Boolean TRUE if the theme is enabled; FALSE otherwise.
  */
 function drupal_theme_access($theme) {
   if (is_object($theme)) {
@@ -70,6 +100,9 @@ function drupal_theme_access($theme) {
   }
   else {
     $themes = list_themes();
+    if (!isset($themes[$theme])) {
+      return FALSE;
+    }
     return !empty($themes[$theme]->status);
   }
 }
@@ -661,14 +694,14 @@ function _theme_build_registry($theme, $base_theme, $theme_engine) {
  *     declare this theme as their base theme.
 */
 function list_themes($refresh = FALSE) {
-  $list = &drupal_static(__FUNCTION__, array());
+  $list = &drupal_static(__FUNCTION__);
 
   if ($refresh) {
-    $list = array();
+    $list = NULL;
     system_list_reset();
   }
 
-  if (empty($list)) {
+  if (!isset($list)) {
     $list = array();
     $themes = array();
     // Extract from the database only when it is available.
@@ -1407,29 +1440,136 @@ function theme_render_template($template_file, $variables) {
 /**
  * Enable a given list of themes.
  *
- * @param $theme_list
- *   An array of theme names.
+ * @param array $theme_list
+ *   An array of theme names to enable.
+ * @param bool $enable_dependencies
+ *   If TRUE, dependencies will automatically be added and enabled in the
+ *   correct order. This incurs a significant performance cost, so use FALSE
+ *   if you know $theme_list is already complete and in the correct order.
+ *
+ * @todo D8: This is almost identical to module_enable() now. Only differences:
+ *   - There is no required default .theme PHP file to load.
+ *   - There is no schema to install.
+ *   - System list, state, theme list, and static resets slightly differ.
+ * @todo hook_themes_installed(), hook_themes_enabled(), etc are not invoked in
+ *   themes, since they are excluded from the hook system.
  */
-function theme_enable($theme_list) {
-  drupal_clear_css_cache();
+function theme_enable($theme_list, $enable_dependencies = TRUE) {
+  if ($enable_dependencies) {
+    // Get all theme data so we can find dependencies and sort.
+    $theme_data = system_rebuild_theme_data();
+    // Create an associative array with weights as values.
+    $theme_list = array_flip(array_values($theme_list));
+
+    while (list($theme) = each($theme_list)) {
+      if (!isset($theme_data[$theme])) {
+        // This theme is not found in the filesystem, abort.
+        return FALSE;
+      }
+      if ($theme_data[$theme]->status) {
+        // Skip already enabled themes.
+        unset($theme_list[$theme]);
+        continue;
+      }
+      $theme_list[$theme] = $theme_data[$theme]->sort;
+
+      // Add dependencies to the list, with a placeholder weight.
+      // The new themes will be processed as the while loop continues.
+      foreach (array_keys($theme_data[$theme]->requires) as $dependency) {
+        if (!isset($theme_list[$dependency])) {
+          $theme_list[$dependency] = 0;
+        }
+      }
+    }
+
+    if (!$theme_list) {
+      // Nothing to do. All themes already enabled.
+      return TRUE;
+    }
+
+    // Sort the theme list by pre-calculated weights.
+    arsort($theme_list);
+    $theme_list = array_keys($theme_list);
+  }
+
+  // Required for schema version checks and constants.
+  include_once DRUPAL_ROOT . '/core/includes/install.inc';
+
+  $themes_installed = array();
+  $themes_enabled = array();
+  $schema_store = drupal_container()->get('keyvalue')->get('system.schema');
   $theme_config = config('system.theme');
-  $disabled_themes = config('system.theme.disabled');
+  $disabled_config = config('system.theme.disabled');
   foreach ($theme_list as $key) {
-    // The value is not used; the weight is ignored for themes currently.
-    $theme_config->set("enabled.$key", 0);
-    $disabled_themes->clear($key);
-    // Install default configuration of the theme.
-    config_install_default_config('theme', $key);
+    // Only process themes that are not already enabled.
+    $enabled = $theme_config->get("enabled.$key") !== NULL;
+    if (!$enabled) {
+      // The value is not used; the weight is ignored for themes currently.
+      $theme_config
+        ->set("enabled.$key", 0)
+        ->save();
+      $disabled_config
+        ->clear($key)
+        ->save();
+
+      // Refresh the system list to include it.
+      system_list_reset();
+      // Load the theme's code.
+      drupal_load('theme', $key);
+      // Refresh the schema to include it.
+      drupal_get_schema(NULL, TRUE);
+      // Update the theme registry to include it.
+      list_themes(TRUE);
+      drupal_theme_rebuild();
+
+      // Allow modules to react prior to the installation of a theme.
+      module_invoke_all('themes_preinstall', array($key));
+
+      // Now install the theme if necessary.
+      if (drupal_get_installed_schema_version($key, TRUE) == SCHEMA_UNINSTALLED) {
+        $version = SCHEMA_INSTALLED;
+
+        // Install default configuration of the theme.
+        config_install_default_config('theme', $key);
+
+        drupal_set_installed_schema_version($key, $version);
+        // Allow the theme to perform install tasks.
+        $function = $key . '_install';
+        if (function_exists($function)) {
+          $function();
+        }
+        // Record the fact that it was installed.
+        $themes_installed[] = $key;
+        watchdog('system', '%theme theme installed.', array('%theme' => $key), WATCHDOG_INFO);
+      }
+
+      // Allow modules to react prior to the enabling of a theme.
+      module_invoke_all('themes_preenable', array($key));
+
+      // Enable the theme.
+      $function = $key . '_enable';
+      if (function_exists($function)) {
+        $function();
+      }
+
+      // Record the fact that it was enabled.
+      $themes_enabled[] = $key;
+      watchdog('system', '%theme theme enabled.', array('%theme' => $key), WATCHDOG_INFO);
+    }
   }
-  $theme_config->save();
-  $disabled_themes->save();
 
-  list_themes(TRUE);
-  menu_router_rebuild();
-  drupal_theme_rebuild();
+  // If any themes were newly installed, invoke hook_themes_installed().
+  if (!empty($themes_installed)) {
+    module_invoke_all('themes_installed', $themes_installed);
+  }
 
-  // Invoke hook_themes_enabled() after the themes have been enabled.
-  module_invoke_all('themes_enabled', $theme_list);
+  // If any themes were newly enabled, invoke hook_themes_enabled().
+  if (!empty($themes_enabled)) {
+    module_invoke_all('themes_enabled', $themes_enabled);
+  }
+
+  drupal_clear_css_cache();
+  return TRUE;
 }
 
 /**
@@ -1450,17 +1590,18 @@ function theme_disable($theme_list) {
   drupal_clear_css_cache();
 
   $theme_config = config('system.theme');
-  $disabled_themes = config('system.theme.disabled');
+  $disabled_config = config('system.theme.disabled');
   foreach ($theme_list as $key) {
     // The value is not used; the weight is ignored for themes currently.
-    $theme_config->clear("enabled.$key");
-    $disabled_themes->set($key, 0);
+    $disabled_config
+      ->set($key, 0)
+      ->save();
+    $theme_config
+      ->clear("enabled.$key")
+      ->save();
   }
-  $theme_config->save();
-  $disabled_themes->save();
 
   list_themes(TRUE);
-  menu_router_rebuild();
   drupal_theme_rebuild();
 
   // Invoke hook_themes_disabled after the themes have been disabled.
diff --git a/core/includes/theme.maintenance.inc b/core/includes/theme.maintenance.inc
index 4b3e80c..6718e87 100644
--- a/core/includes/theme.maintenance.inc
+++ b/core/includes/theme.maintenance.inc
@@ -17,11 +17,6 @@
 function _drupal_maintenance_theme() {
   global $theme, $theme_key, $conf;
 
-  // If $theme is already set, assume the others are set too, and do nothing.
-  if (isset($theme)) {
-    return;
-  }
-
   require_once DRUPAL_ROOT . '/' . variable_get('path_inc', 'core/includes/path.inc');
   require_once DRUPAL_ROOT . '/core/includes/theme.inc';
   require_once DRUPAL_ROOT . '/core/includes/common.inc';
diff --git a/core/lib/Drupal/Core/DrupalKernel.php b/core/lib/Drupal/Core/DrupalKernel.php
index 869d4ee..b0a7947 100644
--- a/core/lib/Drupal/Core/DrupalKernel.php
+++ b/core/lib/Drupal/Core/DrupalKernel.php
@@ -45,7 +45,7 @@ public function registerBundles() {
 
     // @todo Remove the necessity of calling system_list() to find out which
     // bundles exist. See http://drupal.org/node/1331486
-    $modules = array_keys(system_list('module_enabled'));
+    $modules = array_keys(system_list('module'));
     foreach ($modules as $module) {
       $camelized = ContainerBuilder::camelize($module);
       $class = "Drupal\\{$module}\\{$camelized}Bundle";
diff --git a/core/lib/Drupal/Core/ExceptionController.php b/core/lib/Drupal/Core/ExceptionController.php
index cb448de..5d6e6f9 100644
--- a/core/lib/Drupal/Core/ExceptionController.php
+++ b/core/lib/Drupal/Core/ExceptionController.php
@@ -263,9 +263,10 @@ public function on500Html(FlattenException $exception, Request $request) {
       drupal_set_message(t('%type: !message in %function (line %line of %file).', $error), $class);
     }
 
-    drupal_set_title(t('Error'));
     // We fallback to a maintenance page at this point, because the page
     // generation itself can generate errors.
+    drupal_maintenance_theme();
+    drupal_set_title(t('Error'));
     $output = theme('maintenance_page', array('content' => t('The website encountered an unexpected error. Please try again later.')));
 
     $response = new Response($output, 500);
diff --git a/core/modules/block/block.admin.inc b/core/modules/block/block.admin.inc
index 2a17a55..c233ee3 100644
--- a/core/modules/block/block.admin.inc
+++ b/core/modules/block/block.admin.inc
@@ -33,6 +33,9 @@ function block_admin_display($theme = NULL) {
     // If theme is not specifically set, rehash for the current theme.
     $theme = $theme_key;
   }
+  elseif (is_object($theme)) {
+    $theme = $theme->name;
+  }
 
   // Fetch and sort blocks.
   $blocks = block_admin_display_prepare_blocks($theme);
diff --git a/core/modules/block/block.module b/core/modules/block/block.module
index 2978146..ced66f4 100644
--- a/core/modules/block/block.module
+++ b/core/modules/block/block.module
@@ -62,11 +62,21 @@ function block_help($path, $arg) {
     case 'admin/structure/block/add':
       return '<p>' . t('Use this page to create a new custom block.') . '</p>';
   }
-  if ($arg[0] == 'admin' && $arg[1] == 'structure' && $arg['2'] == 'block' && (empty($arg[3]) || $arg[3] == 'list')) {
-    $demo_theme = !empty($arg[4]) ? $arg[4] : variable_get('theme_default', 'stark');
-    $themes = list_themes();
+
+  if ($arg[0] === 'admin' && $arg[1] === 'structure' && $arg['2'] === 'block' && (empty($arg[3]) || $arg[3] === 'list')) {
     $output = '<p>' . t('This page provides a drag-and-drop interface for assigning a block to a region, and for controlling the order of blocks within regions. Since not all themes implement the same regions, or display regions in the same way, blocks are positioned on a per-theme basis. Remember that your changes will not be saved until you click the <em>Save blocks</em> button at the bottom of the page. Click the <em>configure</em> link next to each block to configure its specific title and visibility settings.') . '</p>';
-    $output .= '<p>' . l(t('Demonstrate block regions (@theme)', array('@theme' => $themes[$demo_theme]->info['name'])), 'admin/structure/block/demo/' . $demo_theme) . '</p>';
+    if (!empty($arg[4])) {
+      if (drupal_theme_access($arg[4])) {
+        $demo_theme = $arg[4];
+      }
+    }
+    else {
+      $demo_theme = variable_get('theme_default', 'stark');
+    }
+    if (isset($demo_theme)) {
+      $themes = list_themes();
+      $output .= '<p>' . l(t('Demonstrate block regions (@theme)', array('@theme' => $themes[$demo_theme]->info['name'])), 'admin/structure/block/demo/' . $demo_theme) . '</p>';
+    }
     return $output;
   }
 }
@@ -103,12 +113,10 @@ function block_permission() {
  * Implements hook_menu().
  */
 function block_menu() {
-  $default_theme = variable_get('theme_default', 'stark');
   $items['admin/structure/block'] = array(
     'title' => 'Blocks',
     'description' => 'Configure what block content appears in your site\'s sidebars and other regions.',
     'page callback' => 'block_admin_display',
-    'page arguments' => array($default_theme),
     'access arguments' => array('administer blocks'),
     'file' => 'block.admin.inc',
   );
@@ -141,39 +149,94 @@ function block_menu() {
     'type' => MENU_LOCAL_ACTION,
     'file' => 'block.admin.inc',
   );
-  foreach (list_themes() as $key => $theme) {
-    $items['admin/structure/block/list/' . $key] = array(
-      'title' => check_plain($theme->info['name']),
-      'page arguments' => array($key),
-      'type' => $key == $default_theme ? MENU_DEFAULT_LOCAL_TASK : MENU_LOCAL_TASK,
-      'weight' => $key == $default_theme ? -10 : 0,
-      'access callback' => '_block_themes_access',
-      'access arguments' => array($key),
-      'file' => 'block.admin.inc',
-    );
-    if ($key != $default_theme) {
-      $items['admin/structure/block/list/' . $key . '/add'] = array(
-        'title' => 'Add block',
-        'page callback' => 'drupal_get_form',
-        'page arguments' => array('block_add_block_form'),
-        'access arguments' => array('administer blocks'),
-        'type' => MENU_LOCAL_ACTION,
-        'file' => 'block.admin.inc',
+
+  $items['admin/structure/block/list/default'] = array(
+    'title' => 'Default theme blocks',
+    'type' => MENU_DEFAULT_LOCAL_TASK,
+    'weight' => -10,
+  );
+  $items['admin/structure/block/list/%theme'] = array(
+    'title' => 'Theme blocks',
+    'title callback' => '_theme_menu_title',
+    'title arguments' => array(4),
+    'page callback' => 'block_admin_display',
+    'page arguments' => array(4),
+    'type' => MENU_LOCAL_TASK,
+    'access callback' => '_block_themes_access',
+    'access arguments' => array(4),
+    'file' => 'block.admin.inc',
+  );
+  $items['admin/structure/block/list/%theme/add'] = array(
+    'title' => 'Add block',
+    'page callback' => 'drupal_get_form',
+    'page arguments' => array('block_add_block_form'),
+    'access arguments' => array('administer blocks'),
+    'type' => MENU_LOCAL_ACTION,
+    'file' => 'block.admin.inc',
+  );
+  $items['admin/structure/block/demo/%theme'] = array(
+    'title' => 'Theme block region demo',
+    'title callback' => '_theme_menu_title',
+    'title arguments' => array(4),
+    'page callback' => 'block_admin_demo',
+    'page arguments' => array(4),
+    'type' => MENU_CALLBACK,
+    'access callback' => '_block_themes_access',
+    'access arguments' => array(4),
+    'theme callback' => '_block_custom_theme',
+    'theme arguments' => array(4),
+    'file' => 'block.admin.inc',
+  );
+  return $items;
+}
+
+/**
+ * Implements hook_menu_local_tasks_alter().
+ */
+function block_menu_local_tasks_alter(&$data, $router_item, $root_path) {
+  if ($root_path == 'admin/structure/block' || strpos($root_path, 'admin/structure/block/list') === 0) {
+    // Replace the tab title of the default local task with the name of the
+    // default theme.
+    $themes = list_themes();
+    $default_theme = variable_get('theme_default', 'stark');
+    foreach ($data['tabs'][0] as $i => &$tab) {
+      if (isset($tab['#link']['path'])) {
+        if ($tab['#link']['path'] == 'admin/structure/block/list/default') {
+          $tab['#link']['title'] = $themes[$default_theme]->info['name'];
+        }
+        elseif ($tab['#link']['path'] == 'admin/structure/block/list/%') {
+          $selected_theme_index = $i;
+        }
+      }
+    }
+
+    // Expand the dynamic %theme argument into a tab for each theme.
+    $selected_theme = isset($router_item['original_map'][4]) ? $router_item['original_map'][4] : NULL;
+    foreach ($themes as $theme) {
+      // The default theme is always exposed as default local task already.
+      if ($theme->name === $default_theme) {
+        continue;
+      }
+      // If the current page shows the interface for a selected theme, then the
+      // menu router item with the %theme argument will expose the selected
+      // theme already; do not duplicate that tab, but ensure it appears in a
+      // consistent order when switching between tabs.
+      if ($theme->name === $selected_theme) {
+        $data['tabs'][0][] = $data['tabs'][0][$selected_theme_index];
+        unset($data['tabs'][0][$selected_theme_index]);
+        continue;
+      }
+      $data['tabs'][0][] = array(
+        '#theme' => 'menu_local_task',
+        '#link' => array(
+          'title' => $theme->info['name'],
+          'href' => 'admin/structure/block/list/' . $theme->name,
+        ),
+        '#active' => $theme->name === $selected_theme,
+        '#weight' => $theme->name === $default_theme ? -10 : 0,
       );
     }
-    $items['admin/structure/block/demo/' . $key] = array(
-      'title' => check_plain($theme->info['name']),
-      'page callback' => 'block_admin_demo',
-      'page arguments' => array($key),
-      'type' => MENU_CALLBACK,
-      'access callback' => '_block_themes_access',
-      'access arguments' => array($key),
-      'theme callback' => '_block_custom_theme',
-      'theme arguments' => array($key),
-      'file' => 'block.admin.inc',
-    );
   }
-  return $items;
 }
 
 /**
@@ -208,7 +271,9 @@ function _block_themes_access($theme) {
 function _block_custom_theme($theme = NULL) {
   // We return exactly what was passed in, to guarantee that the page will
   // always be displayed using the theme whose blocks are being configured.
-  return $theme;
+  if (isset($theme->name)) {
+    return $theme->name;
+  }
 }
 
 /**
@@ -273,7 +338,7 @@ function block_page_build(&$page) {
   $all_regions = system_region_list($theme);
 
   $item = menu_get_item();
-  if ($item['path'] != 'admin/structure/block/demo/' . $theme) {
+  if ($item['path'] != 'admin/structure/block/demo/%') {
     // Load all region content assigned via blocks.
     foreach (array_keys($all_regions) as $region) {
       // Assign blocks to region.
@@ -293,8 +358,7 @@ function block_page_build(&$page) {
   }
   else {
     // Append region description if we are rendering the regions demo page.
-    $item = menu_get_item();
-    if ($item['path'] == 'admin/structure/block/demo/' . $theme) {
+    if ($item['path'] == 'admin/structure/block/demo/%') {
       $visible_regions = array_keys(system_region_list($theme, REGIONS_VISIBLE));
       foreach ($visible_regions as $region) {
         $description = '<div class="block-region">' . $all_regions[$region] . '</div>';
@@ -412,6 +476,10 @@ function _block_rehash($theme = NULL) {
   }
   $regions = system_region_list($theme);
 
+  if (is_object($theme)) {
+    $theme = $theme->name;
+  }
+
   // These are the blocks the function will return.
   $blocks = array();
   // These are the blocks defined by code and modified by the database.
diff --git a/core/modules/block/lib/Drupal/block/Tests/BlockAdminThemeTest.php b/core/modules/block/lib/Drupal/block/Tests/BlockAdminThemeTest.php
index c3a220f..ddee5dc 100644
--- a/core/modules/block/lib/Drupal/block/Tests/BlockAdminThemeTest.php
+++ b/core/modules/block/lib/Drupal/block/Tests/BlockAdminThemeTest.php
@@ -37,9 +37,9 @@ function testAdminTheme() {
     $admin_user = $this->drupalCreateUser(array('administer blocks', 'administer themes'));
     $this->drupalLogin($admin_user);
 
-    // Ensure that access to block admin page is denied when theme is disabled.
+    // Ensure the block admin page cannot be accessed for a disabled theme.
     $this->drupalGet('admin/structure/block/list/bartik');
-    $this->assertResponse(403);
+    $this->assertResponse(404);
 
     // Enable admin theme and confirm that tab is accessible.
     theme_enable(array('bartik'));
diff --git a/core/modules/block/lib/Drupal/block/Tests/BlockHiddenRegionTest.php b/core/modules/block/lib/Drupal/block/Tests/BlockHiddenRegionTest.php
index af5acb9..2bf01ed 100644
--- a/core/modules/block/lib/Drupal/block/Tests/BlockHiddenRegionTest.php
+++ b/core/modules/block/lib/Drupal/block/Tests/BlockHiddenRegionTest.php
@@ -65,7 +65,7 @@ function testBlockNotInHiddenRegion() {
     $theme = 'block_test_theme';
     theme_enable(array($theme));
     variable_set('theme_default', $theme);
-    menu_router_rebuild();
+    menu_cache_clear_all();
 
     // Ensure that "block_test_theme" is set as the default theme.
     $this->drupalGet('admin/structure/block');
diff --git a/core/modules/forum/forum.module b/core/modules/forum/forum.module
index f365491..9b9006f 100644
--- a/core/modules/forum/forum.module
+++ b/core/modules/forum/forum.module
@@ -209,7 +209,7 @@ function forum_menu_local_tasks_alter(&$data, $router_item, $root_path) {
           );
         }
       }
-      $data['actions']['output'] = array_merge($data['actions']['output'], $links);
+      $data['actions'] = array_merge($data['actions'], $links);
     }
   }
 }
diff --git a/core/modules/node/node.module b/core/modules/node/node.module
index 2dd1b57..b693e29 100644
--- a/core/modules/node/node.module
+++ b/core/modules/node/node.module
@@ -2062,7 +2062,7 @@ function node_menu_local_tasks_alter(&$data, $router_item, $root_path) {
   if ($root_path == 'admin/content') {
     $item = menu_get_item('node/add');
     if ($item['access']) {
-      $data['actions']['output'][] = array(
+      $data['actions'][] = array(
         '#theme' => 'menu_local_action',
         '#link' => $item,
       );
diff --git a/core/modules/shortcut/lib/Drupal/shortcut/Tests/ShortcutLinksTest.php b/core/modules/shortcut/lib/Drupal/shortcut/Tests/ShortcutLinksTest.php
index 54eeab4..2bee0f6 100644
--- a/core/modules/shortcut/lib/Drupal/shortcut/Tests/ShortcutLinksTest.php
+++ b/core/modules/shortcut/lib/Drupal/shortcut/Tests/ShortcutLinksTest.php
@@ -122,6 +122,7 @@ function testShortcutLinkDelete() {
    */
   function testNoShortcutLink() {
     // Change to a theme that displays shortcuts.
+    theme_enable(array('seven'));
     variable_set('theme_default', 'seven');
 
     $this->drupalGet('page-that-does-not-exist');
diff --git a/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php
index b31d8a0..c0f156e 100644
--- a/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php
@@ -811,11 +811,6 @@ protected function prepareEnvironment() {
     unset($GLOBALS['theme_key']);
     unset($GLOBALS['theme']);
 
-    // Re-initialize the theme to ensure that tests do not see an inconsistent
-    // behavior when calling functions that would initialize the theme if it has
-    // not been initialized yet.
-    drupal_theme_initialize();
-
     // Log fatal errors.
     ini_set('log_errors', 1);
     ini_set('error_log', $this->public_files_directory . '/error.log');
diff --git a/core/modules/simpletest/lib/Drupal/simpletest/UnitTestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/UnitTestBase.php
index 98ed71d..79f7f77 100644
--- a/core/modules/simpletest/lib/Drupal/simpletest/UnitTestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/UnitTestBase.php
@@ -66,6 +66,11 @@ protected function setUp() {
       return FALSE;
     }
 
+    // Re-initialize the theme to ensure that tests do not see an inconsistent
+    // behavior when calling functions that would initialize the theme if it has
+    // not been initialized yet.
+    drupal_theme_initialize();
+
     // Set user agent to be consistent with WebTestBase.
     $_SERVER['HTTP_USER_AGENT'] = $this->databasePrefix;
 
diff --git a/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
index 400d885..de45b78 100644
--- a/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
@@ -720,6 +720,11 @@ protected function setUp() {
       $this->rebuildContainer();
     }
 
+    // Re-initialize the theme to ensure that tests do not see an inconsistent
+    // behavior when calling functions that would initialize the theme if it has
+    // not been initialized yet.
+    drupal_theme_initialize();
+
     // Reset/rebuild all data structures after enabling the modules.
     $this->resetAll();
 
diff --git a/core/modules/system/lib/Drupal/system/Tests/Batch/PageTest.php b/core/modules/system/lib/Drupal/system/Tests/Batch/PageTest.php
index 69dee9c..8f8bdd5 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Batch/PageTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Batch/PageTest.php
@@ -35,8 +35,8 @@ public static function getInfo() {
   function testBatchProgressPageTheme() {
     // Make sure that the page which starts the batch (an administrative page)
     // is using a different theme than would normally be used by the batch API.
+    theme_enable(array('bartik', 'seven'));
     variable_set('theme_default', 'bartik');
-    theme_enable(array('seven'));
     variable_set('admin_theme', 'seven');
     // Log in as an administrator who can see the administrative theme.
     $admin_user = $this->drupalCreateUser(array('view the administration theme'));
diff --git a/core/modules/system/lib/Drupal/system/Tests/System/ThemeTest.php b/core/modules/system/lib/Drupal/system/Tests/System/ThemeTest.php
index 3d0188d..e675843 100644
--- a/core/modules/system/lib/Drupal/system/Tests/System/ThemeTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/System/ThemeTest.php
@@ -206,7 +206,7 @@ function testAdministrationTheme() {
     $this->assertRaw('core/themes/stark', t('Site default theme used on the add content page.'));
 
     // Reset to the default theme settings.
-    variable_set('theme_default', 'bartik');
+    variable_set('theme_default', 'stark');
     $edit = array(
       'admin_theme' => '0',
       'node_admin_theme' => FALSE,
@@ -214,10 +214,10 @@ function testAdministrationTheme() {
     $this->drupalPost('admin/appearance', $edit, t('Save configuration'));
 
     $this->drupalGet('admin');
-    $this->assertRaw('core/themes/bartik', t('Site default theme used on administration page.'));
+    $this->assertRaw('core/themes/stark', t('Site default theme used on administration page.'));
 
     $this->drupalGet('node/add');
-    $this->assertRaw('core/themes/bartik', t('Site default theme used on the add content page.'));
+    $this->assertRaw('core/themes/stark', t('Site default theme used on the add content page.'));
   }
 
   /**
diff --git a/core/modules/system/lib/Drupal/system/Tests/Theme/ThemeTest.php b/core/modules/system/lib/Drupal/system/Tests/Theme/ThemeTest.php
index 484d00b..f4660aa 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Theme/ThemeTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Theme/ThemeTest.php
@@ -141,18 +141,20 @@ function testTemplateOverride() {
    * Test the list_themes() function.
    */
   function testListThemes() {
+    theme_enable(array('test_subtheme'));
     $themes = list_themes();
     // Check if drupal_theme_access() retrieves enabled themes properly from list_themes().
     $this->assertTrue(drupal_theme_access('test_theme'), t('Enabled theme detected'));
-    // Check if list_themes() returns disabled themes.
-    $this->assertTrue(array_key_exists('test_basetheme', $themes), t('Disabled theme detected'));
+
     // Check for base theme and subtheme lists.
     $base_theme_list = array('test_basetheme' => 'Theme test base theme');
     $sub_theme_list = array('test_subtheme' => 'Theme test subtheme');
     $this->assertIdentical($themes['test_basetheme']->sub_themes, $sub_theme_list, t('Base theme\'s object includes list of subthemes.'));
     $this->assertIdentical($themes['test_subtheme']->base_themes, $base_theme_list, t('Subtheme\'s object includes list of base themes.'));
+
     // Check for theme engine in subtheme.
     $this->assertIdentical($themes['test_subtheme']->engine, 'phptemplate', t('Subtheme\'s object includes the theme engine.'));
+
     // Check for theme engine prefix.
     $this->assertIdentical($themes['test_basetheme']->prefix, 'phptemplate', t('Base theme\'s object includes the theme engine prefix.'));
     $this->assertIdentical($themes['test_subtheme']->prefix, 'phptemplate', t('Subtheme\'s object includes the theme engine prefix.'));
@@ -162,6 +164,7 @@ function testListThemes() {
    * Test the theme_get_setting() function.
    */
   function testThemeGetSetting() {
+    theme_enable(array('test_subtheme'));
     $GLOBALS['theme_key'] = 'test_theme';
     $this->assertIdentical(theme_get_setting('theme_test_setting'), 'default value', t('theme_get_setting() uses the default theme automatically.'));
     $this->assertNotEqual(theme_get_setting('subtheme_override', 'test_basetheme'), theme_get_setting('subtheme_override', 'test_subtheme'), t('Base theme\'s default settings values can be overridden by subtheme.'));
diff --git a/core/modules/system/system.admin.inc b/core/modules/system/system.admin.inc
index c55289c..403dd82 100644
--- a/core/modules/system/system.admin.inc
+++ b/core/modules/system/system.admin.inc
@@ -118,8 +118,9 @@ function system_themes_page() {
   uasort($themes, 'system_sort_modules_by_info_name');
 
   $theme_default = variable_get('theme_default', 'stark');
-  $theme_groups  = array();
+  $theme_groups = array('enabled' => array(), 'disabled' => array());
   $admin_theme = variable_get('admin_theme', 0);
+  $admin_theme_options = array();
 
   foreach ($themes as &$theme) {
     if (!empty($theme->info['hidden'])) {
@@ -280,12 +281,10 @@ function system_themes_admin_form_submit($form, &$form_state) {
 function system_theme_enable() {
   if (isset($_REQUEST['theme']) && isset($_REQUEST['token']) && drupal_valid_token($_REQUEST['token'], 'system-theme-operation-link')) {
     $theme = $_REQUEST['theme'];
-    // Get current list of themes.
-    $themes = list_themes();
-
     // Check if the specified theme is one recognized by the system.
-    if (!empty($themes[$theme])) {
+    if (drupal_get_path('theme', $theme)) {
       theme_enable(array($theme));
+      $themes = list_themes();
       drupal_set_message(t('The %theme theme has been enabled.', array('%theme' => $themes[$theme]->info['name'])));
     }
     else {
@@ -330,26 +329,17 @@ function system_theme_disable() {
 function system_theme_default() {
   if (isset($_REQUEST['theme']) && isset($_REQUEST['token']) && drupal_valid_token($_REQUEST['token'], 'system-theme-operation-link')) {
     $theme = $_REQUEST['theme'];
-    // Get current list of themes.
-    $themes = list_themes();
-
     // Check if the specified theme is one recognized by the system.
-    if (!empty($themes[$theme])) {
+    if (drupal_get_path('theme', $theme)) {
+      $themes = list_themes();
       // Enable the theme if it is currently disabled.
-      if (empty($themes[$theme]->status)) {
-       theme_enable(array($theme));
+      if (!isset($themes[$theme])) {
+        theme_enable(array($theme));
+        $themes = list_themes();
       }
       // Set the default theme.
       variable_set('theme_default', $theme);
 
-      // Rebuild the menu. This duplicates the menu_router_rebuild() in
-      // theme_enable(). However, modules must know the current default theme in
-      // order to use this information in hook_menu() or hook_menu_alter()
-      // implementations, and doing the variable_set() before the theme_enable()
-      // could result in a race condition where the theme is default but not
-      // enabled.
-      menu_router_rebuild();
-
       // The status message depends on whether an admin theme is currently in use:
       // a value of 0 means the admin theme is set to be the default theme.
       $admin_theme = variable_get('admin_theme', 0);
@@ -374,14 +364,17 @@ function system_theme_default() {
 /**
  * Form builder; display theme configuration for entire site and individual themes.
  *
- * @param $key
- *   A theme name.
+ * @param $theme
+ *   (optional) A theme object.
+ *
  * @return
  *   The form structure.
+ *
  * @ingroup forms
  * @see system_theme_settings_submit()
  */
-function system_theme_settings($form, &$form_state, $key = '') {
+function system_theme_settings($form, &$form_state, $theme = NULL) {
+  $key = !empty($theme) ? $theme->name : '';
   // Default settings are defined in theme_get_setting() in includes/theme.inc
   if ($key) {
     $var = 'theme_' . $key . '_settings';
diff --git a/core/modules/system/system.api.php b/core/modules/system/system.api.php
index 0f6d668..b598e83 100644
--- a/core/modules/system/system.api.php
+++ b/core/modules/system/system.api.php
@@ -1084,17 +1084,10 @@ function hook_menu_link_delete($link) {
  *
  * @param $data
  *   An associative array containing:
- *   - actions: An associative array containing:
- *     - count: The amount of actions determined by the menu system, which can
- *       be ignored.
- *     - output: A list of of actions, each one being an associative array
- *       as described above.
- *   - tabs: An indexed array (list) of tab levels (up to 2 levels), each
- *     containing an associative array:
- *     - count: The amount of tabs determined by the menu system. This value
- *       does not need to be altered if there is more than one tab.
- *     - output: A list of of tabs, each one being an associative array as
- *       described above.
+ *   - actions: A list of of actions, each one being an associative array
+ *     as described above.
+ *   - tabs: A list of (up to 2) tab levels that contain a list of of tabs, each
+ *     one being an associative array as described above.
  * @param $router_item
  *   The menu system router item of the page.
  * @param $root_path
@@ -1102,7 +1095,7 @@ function hook_menu_link_delete($link) {
  */
 function hook_menu_local_tasks_alter(&$data, $router_item, $root_path) {
   // Add an action linking to node/add to all pages.
-  $data['actions']['output'][] = array(
+  $data['actions'][] = array(
     '#theme' => 'menu_local_task',
     '#link' => array(
       'title' => t('Add new content'),
@@ -1116,7 +1109,7 @@ function hook_menu_local_tasks_alter(&$data, $router_item, $root_path) {
   );
 
   // Add a tab linking to node/add to all pages.
-  $data['tabs'][0]['output'][] = array(
+  $data['tabs'][0][] = array(
     '#theme' => 'menu_local_task',
     '#link' => array(
       'title' => t('Example tab'),
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index 255c669..e158642 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -690,23 +690,21 @@ function system_menu() {
     'file' => 'system.admin.inc',
     'weight' => 20,
   );
-  // Theme configuration subtabs.
   $items['admin/appearance/settings/global'] = array(
     'title' => 'Global settings',
     'type' => MENU_DEFAULT_LOCAL_TASK,
-    'weight' => -1,
+    'weight' => -10,
+  );
+  $items['admin/appearance/settings/%theme'] = array(
+    'title' => 'Theme settings',
+    'title callback' => '_theme_menu_title',
+    'title arguments' => array(3),
+    'page arguments' => array('system_theme_settings', 3),
+    'access callback' => '_system_themes_access',
+    'access arguments' => array(3),
+    'type' => MENU_LOCAL_TASK,
+    'file' => 'system.admin.inc',
   );
-
-  foreach (list_themes() as $key => $theme) {
-    $items['admin/appearance/settings/' . $theme->name] = array(
-      'title' => $theme->info['name'],
-      'page arguments' => array('system_theme_settings', $theme->name),
-      'type' => MENU_LOCAL_TASK,
-      'access callback' => '_system_themes_access',
-      'access arguments' => array($key),
-      'file' => 'system.admin.inc',
-    );
-  }
 
   // Modules.
   $items['admin/modules'] = array(
@@ -1079,6 +1077,41 @@ function system_menu() {
 }
 
 /**
+ * Implements hook_menu_local_tasks_alter().
+ */
+function system_menu_local_tasks_alter(&$data, $router_item, $root_path) {
+  if ($root_path === 'admin/appearance/settings' || $root_path === 'admin/appearance/settings/%') {
+    // Expand the dynamic %theme argument into a tab for each theme.
+    foreach ($data['tabs'][1] as $i => $tab) {
+      if (isset($tab['#link']['path']) && $tab['#link']['path'] == 'admin/appearance/settings/%') {
+        $selected_theme_index = $i;
+        break;
+      }
+    }
+    $themes = list_themes();
+    $selected_theme = isset($router_item['original_map'][3]) ? $router_item['original_map'][3] : NULL;
+    foreach ($themes as $theme) {
+      // If the current page shows the interface for a selected theme, then the
+      // menu router item with the %theme argument will expose the selected
+      // theme already; do not duplicate that tab, but ensure it appears in a
+      // consistent order when switching between tabs.
+      if ($theme->name === $selected_theme) {
+        $data['tabs'][1][] = $data['tabs'][1][$selected_theme_index];
+        unset($data['tabs'][1][$selected_theme_index]);
+        continue;
+      }
+      $data['tabs'][1][] = array(
+        '#theme' => 'menu_local_task',
+        '#link' => array(
+          'title' => $theme->info['name'],
+          'href' => 'admin/appearance/settings/' . $theme->name,
+        ),
+      );
+    }
+  }
+}
+
+/**
  * Page callback; Execute cron tasks.
  *
  * @see system_cron_access().
@@ -2684,6 +2717,7 @@ function system_get_info($type, $name = NULL) {
     }
   }
   else {
+    // @todo Migrate theme info to ModuleInfo implementation.
     $list = system_list($type);
     foreach ($list as $shortname => $item) {
       if (!empty($item->status)) {
@@ -2709,6 +2743,8 @@ function system_get_info($type, $name = NULL) {
  *   returned.
  *
  * @see Drupal\Core\Utility\ModuleInfo
+ *
+ * @todo Merge this helper entirely into system_get_info()?
  */
 function system_get_module_info($property) {
   static $info;
@@ -2921,6 +2957,9 @@ function _system_rebuild_theme_data() {
 
     if (!empty($themes[$key]->info['base theme'])) {
       $sub_themes[] = $key;
+      // Add the defined base theme as dependency to the theme, in order to
+      // re-use the dependency graph resolution of _module_build_dependencies().
+      $themes[$key]->info['dependencies'][] = $themes[$key]->info['base theme'];
     }
     if ($themes[$key]->info['engine'] == 'theme') {
       $filename = dirname($themes[$key]->uri) . '/' . $themes[$key]->name . '.theme';
@@ -2985,30 +3024,36 @@ function _system_rebuild_theme_data() {
  *   Array of all available themes and their data.
  */
 function system_rebuild_theme_data() {
-  $themes = _system_rebuild_theme_data();
-  ksort($themes);
-  // @todo This function has no business in determining/setting the status of
-  //   a theme, but various other functions expect it to return themes with a
-  //   $status property. system_list() stores the return value of this function
-  //   in state, and ensures to set/override the $status property for each theme
-  //   based on the current config. Remove this code when themes have a proper
-  //   installation status.
-  // @see http://drupal.org/node/1067408
-  $enabled_themes = config('system.theme')->get('enabled');
-  $files = array();
-  foreach ($themes as $name => $theme) {
-    $theme->status = (int) isset($enabled_themes[$name]);
-    $files[$name] = $theme->filename;
-  }
-  // Replace last known theme data state.
-  // @todo Obsolete with proper installation status for themes.
-  state()->set('system.theme.data', $themes);
-
-  // Store filenames to allow system_list() and drupal_get_filename() to
-  // retrieve them without having to rebuild or scan the filesystem.
-  state()->set('system.theme.files', $files);
+  $cache = &drupal_static(__FUNCTION__);
+  // Only rebuild once per request. $themes and $cache cannot be combined into
+  // one variable, because $cache is reset by reference from system_list_reset()
+  // during a rebuild.
+  if (!isset($cache)) {
+    $themes = _system_rebuild_theme_data();
+    $files = array();
+    ksort($themes);
+    // Add name, status, and schema version.
+    $enabled_themes = (array) config('system.theme')->get('enabled');
+    $disabled_themes = (array) config('system.theme.disabled')->get();
+    $all_themes = $enabled_themes + $disabled_themes;
+    foreach ($themes as $name => $theme) {
+      $theme->name = $name;
+      $theme->weight = isset($all_themes[$name]) ? $all_themes[$name] : 0;
+      $theme->status = (int) isset($enabled_themes[$name]);
+      $theme->schema_version = SCHEMA_UNINSTALLED;
+      $files[$name] = $theme->filename;
+
+      // Replace last known theme data state.
+      state()->set('system.theme.data.' . $name, $theme);
+    }
+    $themes = _module_build_dependencies($themes);
+    $cache = $themes;
 
-  return $themes;
+    // Store filenames to allow system_list() and drupal_get_filename() to
+    // retrieve them without having to rebuild or scan the filesystem.
+    state()->set('system.theme.files', $files);
+  }
+  return $cache;
 }
 
 /**
@@ -3066,25 +3111,26 @@ function _system_default_theme_features() {
 /**
  * Get a list of available regions from a specified theme.
  *
- * @param $theme_key
- *   The name of a theme.
+ * @param $theme
+ *   A theme object, or the name of a theme.
  * @param $show
  *   Possible values: REGIONS_ALL or REGIONS_VISIBLE. Visible excludes hidden
  *   regions.
  * @return
  *   An array of regions in the form $region['name'] = 'description'.
  */
-function system_region_list($theme_key, $show = REGIONS_ALL) {
-  $themes = list_themes();
-  if (!isset($themes[$theme_key])) {
-    return array();
+function system_region_list($theme, $show = REGIONS_ALL) {
+  if (!is_object($theme)) {
+    $themes = list_themes();
+    if (!isset($themes[$theme])) {
+      return array();
+    }
+    $theme = $themes[$theme];
   }
-
   $list = array();
-  $info = $themes[$theme_key]->info;
   // If requested, suppress hidden regions. See block_admin_display_form().
-  foreach ($info['regions'] as $name => $label) {
-    if ($show == REGIONS_ALL || !isset($info['regions_hidden']) || !in_array($name, $info['regions_hidden'])) {
+  foreach ($theme->info['regions'] as $name => $label) {
+    if ($show == REGIONS_ALL || !isset($theme->info['regions_hidden']) || !in_array($name, $theme->info['regions_hidden'])) {
       $list[$name] = t($label);
     }
   }
diff --git a/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/ThemeTest.php b/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/ThemeTest.php
index b226970..6ab0e74 100644
--- a/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/ThemeTest.php
+++ b/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/ThemeTest.php
@@ -25,8 +25,8 @@ function setUp() {
 
     // Make sure we are using distinct default and administrative themes for
     // the duration of these tests.
+    theme_enable(array('bartik', 'seven'));
     variable_set('theme_default', 'bartik');
-    theme_enable(array('seven'));
     variable_set('admin_theme', 'seven');
 
     // Create and log in as a user who has permission to add and edit taxonomy
diff --git a/core/profiles/standard/standard.install b/core/profiles/standard/standard.install
index 4eeb8d6..270c1f4 100644
--- a/core/profiles/standard/standard.install
+++ b/core/profiles/standard/standard.install
@@ -415,9 +415,6 @@ function standard_install() {
   );
   shortcut_set_save($shortcut_set);
 
-  // Update the menu router information.
-  menu_router_rebuild();
-
   // Enable the admin theme.
   theme_enable(array('seven'));
   variable_set('admin_theme', 'seven');