Python code:

class chatter(models.Model):
   _name = 'mail.chatter'
   _inherit = ['stock.scrap','mail.thread','mail.activity.mixin','mail.alias.mixin']
   _description = 'chatter for scrap form'

XML code:

<record id="view_chatter_inherited" model="ir.ui.view">
         <field name="name">Chatter</field>
         <field name="model">mail.chatter</field>
         <field name="inherit_id" ref="stock.stock_scrap_form_view"/>
         <field name="arch" type="xml">
           <xpath expr="//form/sheet" position="after">
             <div class="oe_chatter">
               <field name="message_follower_ids" widget="mail_followers"/>
               <field name="activity_ids" widget="mail_activity"/>
               <field name="message_ids" widget="mail_thread"/>
             </div>
           </xpath>
         </field>
</record>