fix(audit): iframe with redirect shouldn't be marked as critical

[wardpeet]

Summary

Fixes 302 iframes inside a page marked as critical requests

Related Issues/PRs
#6675

[paulirish]

I'm having a hard time evaluating this PR... This comment describes this original impl, which has changed a lot.

And unfortunately our test page doesn't have an iframe behind a redirect any more. I created a test page (in #7352) but it never gets an entry in the preload audit. (only preconnect)

Going back to the original bug report #6675, the concern is that we suggest to preload an iframe the user is deliberately lazyloading. We could see that an iframe's request was script-initiated and skip those if we want, but I don't think that's neccessary.

At this point I don't know what redirects have to do with this, but maybe there's more context I'm missing.

[kirill-chirkov-at-clouty]

@paulirish I might guess that 302 status on our current iframe (which described in #6675) is pure coincidental, point of issue was that iframe was loaded not with the document but later, JS-initiated, thus not blocking initial parsing and render. Fixing 302 as non-critical request would help in our sole case, but I might guess that won't help where programmaticaly enabled iframe would not give 302 but 200.

[wardpeet]

i'll check it out if it's still a problem ,if not we can just close this one.

[paulirish]

#7352 fixed initiators and redirects. It makes a lot more sense now.

We specifically say that iframes aren't critical.

And we only want critical requests for the user to preload. So if we ever flag a redirect (that eventually is an iframe) in those audits, we have something to fix.

I couldn't get a redirect to show up in preload details. But maybe i wasn't constructing the right situation.

If they'll never show up in preload, then we're done here. :)

[wardpeet]

@paulirish it's not showing up anymore in preload so that's good but the redirect is still marked as a critical request because the resourceType is marked as undefined for a redirect.

I made a repro on glitch
https://erratic-lion.glitch.me

I'm rebasing this branch

[patrickhulce]

oh sorry ward forgot to flush this like weeks ago

[patrickhulce]

LGTM!

[wardpeet]

Fixed comments 😄

[paulirish]

tested this out. lgtm.

redirects to iframes (noncritical) are no longer included as critical. ✅
redirects to scripts (critical) are included as critical requests. ✅

Here's a test run where i added a redirect to a script. you can see it enters into the chain as expected. (this already worked fine in master and continues to work):

And test with redirects before an iframe (master on left, this PR on right):

let's do this.

[wardpeet]

thanks @paulirish !