The Badging API is a proposal for web applications (as defined by the Web App Manifest standard) similar to that of IE's pinned sites with purpose:

• To give the application a small but visible place to subtly notify the user that there is new activity that might require their attention, without showing a full notification.
• To indicate a small amount of additional information, such as an unread count or symbol indicating the type of event.
• To allow the application to convey this information regardless of whether any of the application's windows are open.

Explainer:
https://github.com/WICG/badging/blob/master/explainer.md

Chrome implementation bug:
https://bugs.chromium.org/p/chromium/issues/detail?id=719176