web/web_hideleftmenu/web_hideleftmenu_js.xml

<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data>

        <template id="hideleft_assets_backend" name="web_hideleftmenu assets" inherit_id="web.assets_backend">
            <xpath expr="." position="inside">
                <link rel="stylesheet" href="/web_hideleftmenu/static/src/css/lib.css"/>
                <script type="text/javascript" src="/web_hideleftmenu/static/src/js/lib.js"></script>
            </xpath>
        </template>

    </data>
</openerp>