account-financial-reporting/account_partner_aged_statement_webkit/partner_aged_statement_view.xml

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

    <record id="partner_aged_statement_view" model="ir.ui.view">
      <field name="inherit_id" ref="base.view_partner_form"/>
      <field name="model">res.partner</field>
      <field name="arch" type="xml">
        <xpath expr="//form/*[1]" position="before">
                <header>
                    <button
                            name="action_aged_statement_send"
                            type="object" string="Send Aged Statement"
                            class="oe_highlight"/>
                </header>
        </xpath>
      </field>
    </record>

  </data>
</openerp>