yaltik_odoo_custom/web_widget_url_check/view.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
Copyright 2017 Fabien Bourgeois <fabien@yaltik.com>

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Affero General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU Affero General Public License for more details.

You should have received a copy of the GNU Affero General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.
-->

<odoo>
  <data>
    <template id="assets_backend" name="web_widget_url_check_assets"
      inherit_id="web.assets_backend">
      <xpath expr="." position="inside">
        <script type="text/javascript"
          src="/web_widget_url_check/static/src/js/web_widget_url_check.js"></script>
      </xpath>
    </template>
  </data>
</odoo>