social/website_mass_mailing_name/views/snippets.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- © 2016 Jairo Llopis <jairo.llopis@tecnativa.com>
     License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl). -->

<openerp>
<data>

<template id="mailing_list_subscribe"
          inherit_id="mass_mailing.mailing_list_subscribe">
    <xpath expr="//input[@class='js_subscribe_email form-control']"
           position="before">
        <input
            name="name"
            class="js_subscribe_name form-control"
            placeholder="your name..."/>
    </xpath>
</template>

</data>
</openerp>