[Install Element] Ability to tell if the app is already installed

[vatanaggarwal]

For Google Chat, it would be critical for us to be able to tell if the PWA is already installed before prompting user to install the app. An example of this would be Chat download page https://chat.google.com/download/ which shows a generic GET THE APP link, it would be nice to evaluate if the app is already installed and then show either the install journey or open journey.

[liminzhu]

@vatanaggarwal thanks for the feedback! There is a very relevant proposal called getInstalledRelatedApps (gIRA) that is already supported in Chromium. There is a caveat here that gIRA only supports same origin (e.g. chat.google.com site checking if chat.google.com is already installed) but no cross-origin. If this is needed we should probably think about expanding gIRA or other mechanism.