How facebook app implements draggable floating Button

I´m trying to get some information about how I could implement such a Button like Facebook does in the new version of the app. Actually I am not sure if this button comes from Facebook or from Facebook messenge app but it was the easiest way to have an example of what I would like to achieve. They add a draggable floating Button anywhere you are when getting a new message notification, anybody has and idea about how they achieved that? Thanks in advance. Edited: Toucher: other app which uses what I´d like to achieve. Just below can find a link from Google Play https://play.google.com/store/apps/details?id=com.gau.go.touchhelperex&feature=nav_result#?t=W251bGwsMSwxLDMsImNvbS5nYXUuZ28udG91Y2hoZWxwZXJleCJd