Issue #3347291: Combine field storage and field instance forms

core/lib/Drupal/Core/Entity/EntityForm.php

@@ -138,8 +138,8 @@ protected function init(FormStateInterface $form_state) {
    */
   public function form(array $form, FormStateInterface $form_state) {
     // Add #process and #after_build callbacks.
-    $form['#process'][] = '::processForm';
-    $form['#after_build'][] = '::afterBuild';
+    $form['#process'][] = [$this, 'processForm'];
+    $form['#after_build'][] = [$this, 'afterBuild'];
 
     return $form;
   }