diff --git a/core/lib/Drupal/Core/Extension/ThemeHandler.php b/core/lib/Drupal/Core/Extension/ThemeHandler.php
index cb21836..a6baf9f 100644
--- a/core/lib/Drupal/Core/Extension/ThemeHandler.php
+++ b/core/lib/Drupal/Core/Extension/ThemeHandler.php
@@ -8,14 +8,8 @@
 namespace Drupal\Core\Extension;
 
 use Drupal\Component\Utility\SafeMarkup;
-use Drupal\Core\Asset\AssetCollectionOptimizerInterface;
-use Drupal\Core\Cache\Cache;
 use Drupal\Core\Config\ConfigFactoryInterface;
-use Drupal\Core\Config\ConfigInstallerInterface;
-use Drupal\Core\Config\ConfigManagerInterface;
-use Drupal\Core\Routing\RouteBuilderInterface;
 use Drupal\Core\State\StateInterface;
-use Psr\Log\LoggerInterface;
 
 /**
  * Default theme handler using the config system to store installation statuses.
diff --git a/core/lib/Drupal/Core/Extension/ThemeHandlerInterface.php b/core/lib/Drupal/Core/Extension/ThemeHandlerInterface.php
index 5f3a6cf..5fdceaf 100644
--- a/core/lib/Drupal/Core/Extension/ThemeHandlerInterface.php
+++ b/core/lib/Drupal/Core/Extension/ThemeHandlerInterface.php
@@ -13,6 +13,50 @@
 interface ThemeHandlerInterface {
 
   /**
+   * Installs a given list of themes.
+   *
+   * @param array $theme_list
+   *   An array of theme names.
+   * @param bool $install_dependencies
+   *   (optional) If TRUE, dependencies will automatically be installed 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.
+   *
+   * @return bool
+   *   Whether any of the given themes have been installed.
+   *
+   * @throws \Drupal\Core\Extension\ExtensionNameLengthException
+   *   Thrown when the theme name is to long
+   *
+   * @deprecated in Drupal 8.0.x-dev and will be removed before Drupal 9.0.0.
+   *   Use the theme_installer service instead.
+   *
+   * @see \Drupal\Core\Extension\ThemeInstallerInterface::install
+   */
+  public function install(array $theme_list, $install_dependencies = TRUE);
+
+  /**
+   * Uninstalls a given list of themes.
+   *
+   * Uninstalling a theme removes all related configuration (like blocks) and
+   * invokes the 'themes_uninstalled' hook.
+   *
+   * @param array $theme_list
+   *   The themes to uninstall.
+   *
+   * @throws \InvalidArgumentException
+   *   Thrown when you uninstall an not installed theme.
+   *
+   * @see hook_themes_uninstalled()
+   *
+   * @deprecated in Drupal 8.0.x-dev and will be removed before Drupal 9.0.0.
+   *   Use the theme_installer service instead.
+   *
+   * @see \Drupal\Core\Extension\ThemeInstallerInterface::install
+   */
+  public function uninstall(array $theme_list);
+
+  /**
    * Returns a list of currently installed themes.
    *
    * @return \Drupal\Core\Extension\Extension[]
diff --git a/core/lib/Drupal/Core/Extension/ThemeInstaller.php b/core/lib/Drupal/Core/Extension/ThemeInstaller.php
index 488264a..1bebca2 100644
--- a/core/lib/Drupal/Core/Extension/ThemeInstaller.php
+++ b/core/lib/Drupal/Core/Extension/ThemeInstaller.php
@@ -17,6 +17,9 @@
 use Drupal\Core\State\StateInterface;
 use Psr\Log\LoggerInterface;
 
+/**
+ * Manages theme installation/uninstallation.
+ */
 class ThemeInstaller implements ThemeInstallerInterface {
 
   /**
@@ -171,10 +174,11 @@ public function install(array $theme_list, $install_dependencies = TRUE) {
       // configuration then stop installing.
       $this->configInstaller->checkConfigurationToInstall('theme', $key);
 
-      // The value is not used; the weight is ignored for themes currently.
+      // The value is not used; the weight is ignored for themes currently. Do
+      // not check schema when saving the configuration.
       $extension_config
         ->set("theme.$key", 0)
-        ->save();
+        ->save(TRUE);
 
       // Add the theme to the current list.
       // @todo Remove all code that relies on $status property.
@@ -263,7 +267,9 @@ public function uninstall(array $theme_list) {
       $this->configManager->uninstall('theme', $key);
 
     }
-    $extension_config->save();
+    // Don't check schema when uninstalling a theme since we are only clearing
+    // keys.
+    $extension_config->save(TRUE);
     $this->state->set('system.theme.data', $current_theme_data);