Available in Chrome 44+ (for Android)
The related (Native) app install banner will prompt the user to add your web app to the users device. It will only prompt when a number of criteria have been met:
short_name, 144 pixel icon and a type of 'image/png'
related_applicationssection with an object that has the 'type': 'play' and a Google Play Store package ID.
To see if this example works, come back in another day and you will see the banner.
For testing we encourage you to force the banner to appear by setting the chrome://flags/#bypass-app-banner-engagement-checks flag.