This feature started on the date: 2016-06-01 with this intro:
Web Share Target is a proposed web API to enable a web site to receive shared data from other sites or apps. Many modern operating systems have a “share” concept, where the user gets to pick an app to receive the shared data. The goal is to allow web apps to appear in the UI for picking an app to share to.
In combination with the Web Share API (being proposed in parallel), this would allow cross-sharing between websites on any platform (even those without a native sharing system).
This is a product of the Ballista project, which aims to explore website-to-website and website-to-native interoperability.
The last change is today with chromestatus webpage.
About the Web Share Target.