diff --git a/core/modules/block/src/Controller/BlockController.php b/core/modules/block/src/Controller/BlockController.php
index 7f75d0b..effa842 100644
--- a/core/modules/block/src/Controller/BlockController.php
+++ b/core/modules/block/src/Controller/BlockController.php
@@ -54,7 +54,6 @@ public static function create(ContainerInterface $container) {
    *   A #type 'page' render array containing the block region demo.
    */
   public function demo($theme) {
-    // Deny access if the theme is not installed or not found.
     if (!$this->themeHandler->hasUi($theme)) {
       throw new NotFoundHttpException();
     }
diff --git a/core/modules/block/src/Controller/BlockListController.php b/core/modules/block/src/Controller/BlockListController.php
index b0c5e3f..6185c90 100644
--- a/core/modules/block/src/Controller/BlockListController.php
+++ b/core/modules/block/src/Controller/BlockListController.php
@@ -57,7 +57,6 @@ public static function create(ContainerInterface $container) {
    */
   public function listing($theme = NULL, Request $request = NULL) {
     $theme = $theme ?: $this->config('system.theme')->get('default');
-    // Deny access if the theme is not installed or not found.
     if (!$this->themeHandler->hasUi($theme)) {
       throw new NotFoundHttpException();
     }
diff --git a/core/modules/block/src/Tests/BlockUiTest.php b/core/modules/block/src/Tests/BlockUiTest.php
index 5828189..4d0f03a 100644
--- a/core/modules/block/src/Tests/BlockUiTest.php
+++ b/core/modules/block/src/Tests/BlockUiTest.php
@@ -145,12 +145,11 @@ function testBlockAdminUiPage() {
     // theme and place the local tasks block.
     $this->assertTrue(\Drupal::service('theme_handler')->themeExists('classy'), 'The classy base theme is enabled');
     $this->drupalPlaceBlock('local_tasks_block', ['region' => 'header']);
-    \Drupal::service('theme_installer')->install(['stable']);
-    \Drupal::service('theme_installer')->install(['test_theme']);
+    \Drupal::service('theme_installer')->install(['stable', 'stark']);
     $this->drupalGet('admin/structure/block');
     $theme_handler = \Drupal::service('theme_handler');
     $this->assertLink($theme_handler->getName('classy'));
-    $this->assertLink($theme_handler->getName('test_theme'));
+    $this->assertLink($theme_handler->getName('stark'));
     $this->assertNoLink($theme_handler->getName('stable'));
 
     $this->drupalGet('admin/structure/block/list/stable');
diff --git a/core/modules/system/src/Controller/ThemeController.php b/core/modules/system/src/Controller/ThemeController.php
index 5f56052..d54cd91 100644
--- a/core/modules/system/src/Controller/ThemeController.php
+++ b/core/modules/system/src/Controller/ThemeController.php
@@ -30,26 +30,16 @@ class ThemeController extends ControllerBase {
   protected $themeHandler;
 
   /**
-   * The route builder service.
-   *
-   * @var \Drupal\Core\Routing\RouteBuilderInterface
-   */
-  protected $routeBuilder;
-
-  /**
    * Constructs a new ThemeController.
    *
    * @param \Drupal\Core\Extension\ThemeHandlerInterface $theme_handler
    *   The theme handler.
-   * @param \Drupal\Core\Routing\RouteBuilderInterface $route_builder
-   *   The route builder.
    * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
    *   The config factory.
    */
-  public function __construct(ThemeHandlerInterface $theme_handler, RouteBuilderInterface $route_builder, ConfigFactoryInterface $config_factory) {
+  public function __construct(ThemeHandlerInterface $theme_handler,ConfigFactoryInterface $config_factory) {
     $this->themeHandler = $theme_handler;
     $this->configFactory = $config_factory;
-    $this->routeBuilder = $route_builder;
   }
 
   /**
@@ -58,7 +48,6 @@ public function __construct(ThemeHandlerInterface $theme_handler, RouteBuilderIn
   public static function create(ContainerInterface $container) {
     return new static(
       $container->get('theme_handler'),
-      $container->get('router.builder'),
       $container->get('config.factory')
     );
   }
@@ -183,8 +172,6 @@ public function setDefaultTheme(Request $request) {
         // Set the default theme.
         $config->set('default', $theme)->save();
 
-        $this->routeBuilder->setRebuildNeeded();
-
         // 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.
diff --git a/core/modules/system/src/Form/ThemeSettingsForm.php b/core/modules/system/src/Form/ThemeSettingsForm.php
index a782e15..7f02517 100644
--- a/core/modules/system/src/Form/ThemeSettingsForm.php
+++ b/core/modules/system/src/Form/ThemeSettingsForm.php
@@ -110,7 +110,6 @@ public function buildForm(array $form, FormStateInterface $form_state, $theme =
 
     // Default settings are defined in theme_get_setting() in includes/theme.inc
     if ($theme) {
-      // Deny access if the theme is not installed or not found.
       if (!$this->themeHandler->hasUi($theme)) {
         throw new NotFoundHttpException();
       }
diff --git a/core/modules/system/src/Tests/System/ThemeTest.php b/core/modules/system/src/Tests/System/ThemeTest.php
index 2f636d9..278353d 100644
--- a/core/modules/system/src/Tests/System/ThemeTest.php
+++ b/core/modules/system/src/Tests/System/ThemeTest.php
@@ -54,7 +54,7 @@ function testThemeSettings() {
     $this->assertResponse(404, 'The theme settings form URL for a non-existent theme could not be found.');
     $this->assertTrue(\Drupal::service('theme_installer')->install(['stable']));
     $this->drupalGet('admin/appearance/settings/stable');
-    $this->assertResponse(404, 'The theme settings form URL for a hidden theme are unavailable.');
+    $this->assertResponse(404, 'The theme settings form URL for a hidden theme is unavailable.');
 
     // Specify a filesystem path to be used for the logo.
     $file = current($this->drupalGetTestFiles('image'));
@@ -194,7 +194,7 @@ function testThemeSettings() {
     $this->assertNoFieldByName('logo_path');
     $this->drupalPostForm(NULL, [], t('Save configuration'));
 
-    // Ensure only vlaid themes are listed in the local tasks.
+    // Ensure only valid themes are listed in the local tasks.
     $this->drupalPlaceBlock('local_tasks_block', ['region' => 'header']);
     $this->drupalGet('admin/appearance/settings');
     $theme_handler = \Drupal::service('theme_handler');
@@ -209,7 +209,7 @@ function testThemeSettings() {
     $this->drupalGet('admin/appearance/settings');
     $this->assertLink($theme_handler->getName('stable'));
     $this->drupalGet('admin/appearance/settings/stable');
-    $this->assertResponse(200, 'The theme settings form URL for a hidden theme that is the admin theme are avialable.');
+    $this->assertResponse(200, 'The theme settings form URL for a hidden theme that is the admin theme is available.');
   }
 
   /**
@@ -277,7 +277,7 @@ function testAdministrationTheme() {
   function testSwitchDefaultTheme() {
     /** @var \Drupal\Core\Extension\ThemeHandlerInterface $theme_handler */
     $theme_handler = \Drupal::service('theme_handler');
-    // First, Install Stark and set it as the default theme programmatically.
+    // First, install Stark and set it as the default theme programmatically.
     $theme_handler->install(array('stark'));
     $theme_handler->setDefault('stark');