@since Method available since Release 3.6.0
string $message:
protected function showExtensionNotLoadedMessage($extension, $message = '') {
  if (isset($this->missingExtensions[$extension])) {
    return;
  }
  if (!empty($message)) {
    $message = ' ' . $message;
  }
  $this
    ->showMessage('The ' . $extension . ' extension is not loaded.' . $message . "\n", FALSE);
  $this->missingExtensions[$extension] = TRUE;
}