:bug IFrame placeholder assertion fix

[acsant]

Instructions:

• Placeholder is null on layoutCallback
  • Call to updateLayoutBox in custom-element causes the layoutCallback on the amp-iframe, however this.placeholder_ is null - the context here seems to be different compared to when the IFrame was first rendered and the first layoutCallback was executed.

this.assertPosition above fails because this.placeholder_ is null

After adding the calls to this.getPlaceholder() on layoutCallback:

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[aghassemi]

Thanks @acsant, really appreciate the initiative, we love contributions in AMP.

I assume this is for #19705 (comment) ?

I like to dig a bit deeper on the root cause of this. The properties you are setting in layoutCallback are already set in buildCallback and we should never get to a case where buildCallback is not called before layoutCallback. We need to fix the root cause of this.

Are you by any chance using amp-lightbox-gallery in this page? There was an issue where including that extensions was causing some race conditions in our component life-cycle which was fixed by #19778 couple of days ago ( not in production yet, but should be in Dev Channel - you can enable dev channel by visiting https://cdn.ampproject.org/experiments.html )

It would be great if you can test your page with Dev Channel enabled and let me know if issue is still there.

[eveyiyuan]

@aghassemi We are using amp-lightbox-gallery on this page. Thanks for the advice! Enabling Dev Channel seems to have fixed the issue! At least I haven't been able to reproduce it since enabling it.

[aghassemi]

@eveyiyuan Awesome! Thanks for confirming. That fix will be in production next Tuesday Dec 18.

[aghassemi]

@acsant @eveyiyuan Unrelated to this thread but since you are heavily using amp-lightbox-gallery, I wanted to mention that we have been working on making "swipe to dismiss" interaction much more smooth and native-looking recently. It will launch soon but if you like to take a look and give us feedback, you can see it here: https://amp-polish.firebaseapp.com/examples/article-with-lightbox-2.0-gallery.amp.html (on mobile, use swipe up/down gesture on lightboxed images to close the lightbox)

[aghassemi]

Closing per discussions above.