Как добавить МЕТА-тег в Drupal 8?

Используем старый, добрый hook_page_attachments_alter():

function THEME_page_attachments_alter(array &$page) {
  $meta = array(
    'ie_chrome' => array(
      '#tag' => 'meta',
      '#weight' => -1000,
      '#attributes' => array(
        'http-equiv' => 'X-UA-Compatible',
        'content' => 'IE=edge, chrome=1',
      ),
    ),
    'viewport' => array(
      '#tag' => 'meta',
      '#attributes' => array(
        'name' => 'viewport',
        'content' => 'width=device-width, initial-scale=1, maximum-scale=1, user-scalable=no',
      ),
    ),
  );
  foreach ($meta as $key => $value) {
    $page['#attached']['html_head'][] = [$value, $key];
  }
}