Drupal 8 - Adding custom Views query plugin which implements new aggregation method (SUM DISTINCT)

CustomSql.php

<?php
/**
 * @file
 * Contains \Drupal\my_module\Plugin\views\query\CustomSql.
 */

namespace Drupal\my_module\Plugin\views\query;

use Drupal\views\Plugin\views\query\Sql;

/**
 * Views query plugin for an custom SQL query.
 *
 * @ingroup views_query_plugins
 *
 * @ViewsQuery(
 *   id = "views_custom_query",
 *   title = @Translation("SQL Custom Query"),
 *   help = @Translation("Query will be generated and run using the Drupal database API.")
 * )
 */
class CustomSql extends Sql {

  /**
   * {@inheritdoc}
   */
  public function getAggregationInfo() {
    $aggregation_info = parent::getAggregationInfo();

    $aggregation_info += [
      'sum_distinct' => [
        'title' => $this->t('Sum DISTINCT'),
        'method' => 'aggregationMethodDistinct',
        'handler' => [
          'argument' => 'groupby_numeric',
          'field' => 'numeric',
          'filter' => 'groupby_numeric',
          'sort' => 'groupby_numeric',
        ],
      ],
    ];

    return $aggregation_info;
  }

}

my_module.module

/**
 * @implements hook_views_data_alter().
 *
 * @param array $data
 */
function my_module_views_data_alter(array &$data) {
  if (isset($data['my_table'])) {
    $data['my_table']['table']['base']['query_id'] = 'views_custom_query';
  }
}

Easiest way to implement new Views aggregation method. Valid until https://www.drupal.org/node/2662548 is implemented.