eiru_tools/templates.xml

<openerp>
    <data>
        <template id="eiru_tools" inherit_id="web.assets_backend">
            <xpath expr="." position="inside">
                <link rel="stylesheet" href="/eiru_tools/static/src/css/tools.css" />
                <script type="text/javascript" src="/eiru_tools/static/src/js/tools.js" />
            </xpath>
        </template>
    </data>
</openerp>