Restore the missing custom text area plugin.

lib/Drupal/views/Plugin/views/area/TextCustom.php

+<?php
+
+/**
+ * @file
+ * Definition of Drupal\views\Plugin\views\area\TextCustom.
+ */
+
+namespace Drupal\views\Plugin\views\area;
+
+use Drupal\Core\Annotation\Plugin;
+
+/**
+ * Views area text handler.
+ *
+ * @ingroup views_area_handlers
+ */
+
+/**
+ * @Plugin(
+ *   plugin_id = "text_custom"
+ * )
+ */
+class TextCustom extends AreaPluginBase {
+
+  function option_definition() {
+    $options = parent::option_definition();
+    unset($options['format']);
+    return $options;
+  }
+
+  function options_form(&$form, &$form_state) {
+    parent::options_form($form, $form_state);
+
+    // Alter the form element, to be a regular text area.
+    $form['content']['#type'] = 'textarea';
+    unset($form['content']['#format']);
+    unset($form['content']['#wysiwyg']);
+  }
+
+  // Empty, so we don't inherit options_submit from the parent.
+  function options_submit(&$form, &$form_state) {
+  }
+
+  function render($empty = FALSE) {
+    if (!$empty || !empty($this->options['empty'])) {
+      return $this->render_textarea_custom($this->options['content']);
+    }
+
+    return '';
+  }
+
+  /**
+   * Render a text area with filter_xss_admin.
+   */
+  function render_textarea_custom($value) {
+    if ($value) {
+      if ($this->options['tokenize']) {
+        $value = $this->view->style_plugin->tokenize_value($value, 0);
+      }
+      return $this->sanitize_value($value, 'xss_admin');
+    }
+  }
+
+}

modules/views.views.inc

@@ -57,14 +57,13 @@ function views_views_data() {
     ),
   );
 
-  // @todo: this class seems to be missing.
-//  $data['views']['area_text_custom'] = array(
-//    'title' => t('Unfiltered text'),
-//    'help' => t('Add unrestricted, custom text or markup. This is similar to the custom text field.'),
-//    'area' => array(
-//      'handler' => 'views_handler_area_text_custom',
-//    ),
-//  );
+  $data['views']['area_text_custom'] = array(
+    'title' => t('Unfiltered text'),
+    'help' => t('Add unrestricted, custom text or markup. This is similar to the custom text field.'),
+    'area' => array(
+      'plugin_id' => 'text_custom',
+    ),
+  );
 
   $data['views']['view'] = array(
     'title' => t('View area'),