How to get number of search results?

I need a getter for the number of search results. The workaround I used in past was wonky from first day as taking the number of search results from a global pager variable is really not the cleanest code...

/**
 * Implements hook_preprocess_search_results().
 *
 * Collects and adds the number of search results to the head.
 */
function google_analytics_preprocess_search_results(&$variables) {
  // There is no search result $variable available that hold the number of items
  // found. But the pager item mumber can tell the number of search results.
  global $pager_total_items;

  $page['#attached']['js'][] = array(
    'data' => 'window.googleanalytics_search_results = ' . intval($pager_total_items[0]) . ';',
    'type' => 'inline',
    'group' => JS_LIBRARY-1,
  );
  drupal_render($page);
}

Can you share how I'm able to get the number in hook_page_alter(), please?

Something like SearchResult::getNumberOfItems would be great. Other search modules should be able to reuse this so I'm able to get this from all modules the same way without adding special handling for every module.