Description:
http://forum.xda-developers.com/showpost.php?p=70008707&postcount=1959
As far as App preview messages, that's located under Settings > Google. When adblocking is enabled for Google Play Services, it says there is no internet connection. With adblocking disabled, it works properly and enables the feature for receiving Allo messages without requiring Allo to be installed.
Description:
http://forum.xda-developers.com/showpost.php?p=70008707&postcount=1959