base_location/views/res_country_view.xml

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

        <record id="view_country_search" model="ir.ui.view">
            <field name="name">res.country.search</field>
            <field name="model">res.country</field>
            <field name="arch" type="xml">
                <search string="Country">
                    <field name="name"/>
                    <field name="code"/>
                </search>
            </field>
        </record>

    </data>
</openerp>