Issue #2008976 by InternetDevels: Replace theme() with drupal_render() in ckeditor module.

core/modules/ckeditor/ckeditor.admin.inc

@@ -58,7 +58,12 @@ function theme_ckeditor_settings_toolbar($variables) {
       $value = $button['image_alternative' . $rtl];
     }
     elseif (isset($button['image'])) {
-      $value = theme('image', array('uri' => $button['image' . $rtl], 'title' => $button['label']));
+      $image = array(
+        '#theme' => 'image',
+        '#uri' => $button['image' . $rtl],
+        '#title' => $button['label'],
+      );
+      $value = drupal_render($image);
     }
     else {
       $value = '?';

core/modules/ckeditor/lib/Drupal/ckeditor/Plugin/Editor/CKEditor.php

@@ -51,7 +51,11 @@ public function getDefaultSettings() {
   public function settingsForm(array $form, array &$form_state, EditorEntity $editor) {
     $module_path = drupal_get_path('module', 'ckeditor');
     $manager = drupal_container()->get('plugin.manager.ckeditor.plugin');
-
+    $ckeditor_settings_toolbar = array(
+      '#theme' => 'ckeditor_settings_toolbar',
+      '#editor' => $editor,
+      '#plugins' => $manager->getButtonsPlugins($editor),
+    );
     $form['toolbar'] = array(
       '#type' => 'container',
       '#attached' => array(
@@ -60,7 +64,7 @@ public function settingsForm(array $form, array &$form_state, EditorEntity $edit
           array(
             'type' => 'setting',
             'data' => array('ckeditor' => array(
-              'toolbarAdmin' => theme('ckeditor_settings_toolbar', array('editor' => $editor, 'plugins' => $manager->getButtonsPlugins($editor))),
+              'toolbarAdmin' => drupal_render($ckeditor_settings_toolbar),
             )),
           )
         ),