Google's Gmail app for Android has remained an ad-free sanctuary, but code uncovered by Android Police in an APK teardown of the application's latest version hints that circumstances might change. Buried within the the program is a new library called "ads," along with messages, functions and classes mentioning advertisements. What's more, a "ShowAdPreferenceManager()" function routes users to the ad settings page for their very own Google account. Its not clear if sponsored bits will make it into the promotions folder just like the web version of Mountain View's inbox, but the clues suggest you should brace yourself to see some marketing relatively soon.