Users cannot tab out of a Flutter web app that has been embedded in an iframe. It seems that Flutter web is somehow hogging the tab event, and preventing it (without taking into consideration that it might be iframed).

See an example here:

https://jsfiddle.net/ditman/v5jhx0zo

(In the jsfiddle above, there's a "normal" commented-out iframe that displays the expected behavior; users may tab out of it)

((/cc @skeswa))