odoo/addons/project/res_partner_view.xml

<?xml version="1.0"?>
<openerp>
    <data>

        <record id="res_partner_view_task_tree" model="ir.ui.view">
            <field name="name">res.partner.project.task.tree</field>
            <field name="model">project.task</field>
            <field name="arch" type="xml">
                <tree string="Tasks">
                    <field name="name"/>
                    <field name="user_id"/>
                    <field name="date_deadline"/>
                    <field name="state" invisible="1"/>
                    <button name="do_open" states="pending,draft,done,cancelled" string="Start Task" type="object" icon="gtk-media-play" help="For changing to open state" invisible="context.get('set_visible',False)"/>
                    <button name="action_close" states="draft,pending,open" string="Done" type="object" icon="terp-dialog-close" help="For changing to done state"/>
                </tree>
            </field>
        </record>

        <record id="action_res_partner_tasks_summary" model="ir.actions.act_window">
            <field name="name">Tasks</field>
            <field name="res_model">project.task</field>
            <field name="view_type">form</field>
            <field name="view_mode">tree,form,calendar</field>
            <field name="context">{'search_default_partner_id': [active_id], 'default_partner_id': active_id}</field>
            <field name="view_id" ref="res_partner_view_task_tree"/>
        </record>

        <record id="view_res_partner_task_search_form_group" model="ir.ui.view">
            <field name="name">res.partner.task.search.form.group</field>
            <field name="model">project.task</field>
            <field name="inherit_id" ref="project.view_task_search_form"/>
            <field name="arch" type="xml">
                <field name="project_id" position="before">
                    <field name="partner_id"/>
                </field>
            </field>
        </record>

         <!--  Partners inherited form -->
        <record id="view_task_partner_info_form" model="ir.ui.view">
            <field name="name">res.partner.task.buttons</field>
            <field name="model">res.partner</field>
            <field name="inherit_id" ref="base.view_partner_form"/>
            <field name="priority" eval="30"/>
            <field name="arch" type="xml">
                <xpath expr="//div[@name='buttons']" position="inside">
                    <button type="action"
                        name="%(project.action_res_partner_tasks_summary)d"
                        string="Tasks"
                        groups="project.group_project_user" />
                </xpath>
            </field>
       </record>

   </data>
</openerp>