I'd be curious to know if there are any infobars that appear before a page has completed navigation. If there aren't, we could block or immediately dismiss any infobars that are triggered during a navigation. Though, ideally the controller of the infobar is watching for this and wouldn't event trigger.

This seems like a problem that would persist into the new infrastructure; I'm not convinced this is necessarily tied to native/desktop code. In any case we should discuss possible solutions now so that changes we make going forward account for this.

Issue 816603 has been merged into this issue.

I suspect there is another bug on this.

We can indeed show infobars while a load is pending.  In general, the solution is probably that at the time of an infobar's creation, instead of auto-fetching the ID the infobar should be associated with, it should explicitly specify which navigation it should be associated with.

This is easy to repro if using the experiment ConsumeGestureOnNavigation and the popup blocker:

document.getElementById('link').click();
window.open();

The experiment will cause the popup to be blocked, and the infobar will persist into whatever #link points to.

As an aside: I think it makes more sense to dismiss open infobars (if appropriate) when the navigation commits than to avoid showing them if there is an ongoing navigation. Javascript can do complicated things like start and stop navigations at will and I'd be nervous about having untrusted JS (potentially) in control of when infobars can appear.