eiru_image_optimizer/templates.xml

<openerp>
    <data>
         <template id="eiru_image_optimizer.assets" inherit_id="web.assets_backend">
            <xpath expr="." position="inside">
                <script type="text/javascript" src="/eiru_image_optimizer/static/src/lib/compress.js" /> 
                <script type="text/javascript" src="/eiru_image_optimizer/static/src/js/main.js" />
            </xpath>
        </template>
    </data>
</openerp>