Our neat <legend> labels are no longer shown in Chrome (55.0.2883.35) and friends. Other form elements shift around in confusing ways. This definitely was not happening a couple weeks ago.
Chrome 55 went stable on Thursday, so this suddenly is a bit more pressing. (I only noticed on Saturday, because the original schedule said it'll be next Tuesday, and I thought it can be trusted.) I'll have the fixes SWAT-deployed tomorrow.
(Upstream task got merged into https://bugs.chromium.org/p/chromium/issues/detail?id=670837 for some reason.)
(Of course I7513c3233b07780bab7a90de8a3b249a8d33448f is the wrong Change-Id, the right one is I73f95965694ec7fb0fa9a474742286e1105e5c85. I made a mistake when copy-pasting into the commit message. Corrected in PS2.)
As I understand it Chrome 55 has an issue with the <legend/> tag and the patches above change OOJS/ui to generate a <div/> instead. I can see how it can lead to other breakages for anything that assumes a legend element (skin, gadgets, whatever extension relying on it etc).