The Chrome team at Google has announced that starting with Chrome 68, the banner to prompt users to add a site to their Home screen will be changing. Today, when you visit a site and are prompted to add it to your Home screen, it is a rather large banner. Starting with Chrome 68, this will be displayed in a mini bar at the bottom of the display.
The goal of all of this is to eventually have an install button option on the omni bar in Chrome and this is a stepping stone to that eventuality.
Today, in Chrome 67, when you visit a site that has the criteria met for providing the add to Home screen prompt, you will see a banner at the bottom of a page. See the screenshot below for Google+.
Starting with Chrome 68, it will be presented as a mini bar option like this sample below provided by Google:
As for when we will see this, that should be next month. 68 is slated to move into the various respective platform beta builds any time now with a final release expected to be on or around July 24th.