This is a demo for the non-cookie Storage Access API extension. See the related blog post and spec.
  1. Be sure test-third-party-cookie-phaseout is enabled and restart your browser if needed.
  2. Open the iframe site in its own tab and click somewhere on the page to register user interaction. It should say 'Connected'.
  3. In this window, type some message in the box and click 'Send' below and approve the permissions prompt.
  4. In the other window it should now say 'Connected: ' followed by the same message.
  5. The message was shared via Broadcast Channel using the SAA handle to access unpartitioned storage.
  6. You can find the code for this site here, and the iframe here.