Adding Google Remarketing Script tags to Drupal 7 website
I think you are looking for the Google Adwords Remarketing module. Here is a quote about it (from the module's project page):

Adds the Google Adwords Remarketing web statistics tracking system to your website.
NB - Google now has another (easier) method for using Remarketing tags. If your Adwords account is linked to your Google Analytics account you can enable the tag by installing the Google Analytics module and ticking a tick box under the Google Analytics Drupal admin page - see attached image.
This tick box causes a slight alteration in the GA tag which is needed by Google Remarketing.