apply brave UA whitelist to first-party subresources
apply brave UA whitelist to first-party subresources

fix #10800

Test Plan:
load adobe.com within Brave
open the developer tools via "option + command + I"
select the "Network" tab and reload adobe.com via "command + r"
select on the first resource and you'll notice the correct Brave Chrome/60.0.3112.101 UA
select another resource that's underneath the first one and is from Host:www.adobe.com
the Brave UA should be there

luixxiul/browser-laptop,diasdavid/browser-laptop,diasdavid/browser-laptop,luixxiul/browser-laptop,diasdavid/browser-laptop,luixxiul/browser-laptop,diasdavid/browser-laptop,luixxiul/browser-laptop