magento-test/app/code/Magento/Theme/etc/indexer.xml

<?xml version="1.0"?>
<!--
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
-->
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:noNamespaceSchemaLocation="urn:magento:framework:Indexer/etc/indexer.xsd">
    <indexer id="design_config_grid" view_id="design_config_dummy" class="Magento\Theme\Model\Indexer\Design\Config" primary="design_config">
        <title translate="true">Design Config Grid</title>
        <description translate="true">Rebuild design config grid index</description>

        <fieldset name="design_config" source="Magento\Theme\Model\ResourceModel\Design\Config\Scope\Collection"
                  provider="Magento\Theme\Model\Indexer\Design\Config\FieldsProvider">
            <field name="store_website_id" xsi:type="filterable" dataType="int"/>
            <field name="store_group_id" xsi:type="filterable" dataType="int"/>
            <field name="store_id" xsi:type="filterable" dataType="int"/>
        </fieldset>
        <saveHandler class="Magento\Theme\Model\Indexer\Design\IndexerHandler"/>
        <structure class="Magento\Framework\Indexer\GridStructure"/>
    </indexer>
</config>