It isn’t incorporated with any extra plugin. What you should do firstly is to enable header contact info by going to Appearance > Customize > Sydney Pro: Extra options > Header contact info; and hit the save button.
Secondly, you have to create social menu in the custom menu (Appearance > Menus). Create a new menu (you can use any name), then use Custom Links type of menu in the options listed in the left site of menu composer box. In the URL field, enter your social profile URL address, for example: http://facebook.com/yourbusinesspage. In the Navigation Label field, just enter Facebook or any name that you wish. After you’ve done creating your last social menu item, then tick the “Header social” checkbox in the “Menu Settings” section. Lastly, save menu.