Extract simple workers common code into a base class [PREMIUM-4]

lib/Cron/Workers/KeyCheck/SendingServiceKeyCheck.php

@@ -0,0 +1,22 @@
+<?php
+namespace MailPoet\Cron\Workers\KeyCheck;
+
+use MailPoet\Mailer\Mailer;
+use MailPoet\Services\Bridge;
+
+if(!defined('ABSPATH')) exit;
+
+class SendingServiceKeyCheck extends KeyCheckWorker {
+  const TASK_TYPE = 'sending_service_key_check';
+
+  function checkProcessingRequirements() {
+    return Bridge::isMPSendingServiceEnabled();
+  }
+
+  function checkKey() {
+    $mailer_config = Mailer::getMailerConfig();
+    $result = $this->bridge->checkMSSKey($mailer_config['mailpoet_api_key']);
+    $this->bridge->updateSubscriberCount($result);
+    return $result;
+  }
+}