bug#52375: webkitgtk page crashes on core-updates-frozen

[Jack Hill]

Hi Guix,

With core-updates-frozen commit e080e35dc1f012fa57a8e77759f933abdc3b8fc2 
certain pages cause tabs to crash in webkitgtk browsers (I've tested with 
epiphany, vimb, and luakit). The problem does not occur on current master, 
0a9c946df9686f1610f7684492baabf0719c0164.

An example of a page the works:

https://en.wiktionary.org/wiki/edification

An example of a page that doesn't work:

https://en.wiktionary.org/wiki/edify

I was not able to notice a difference in messages when running the 
browsers from a terminal between master and core-updates-frozen.

On both branches I do see "WebKit wasn't able to find a WebVTT encoder. 
Not continuing without platform support for subtitles" when the tab 
crashes, so I wonder if there is a gstreamer compatibility problem 
(perhaps to do with libsoup versions). However, this could be a red 
herring.

Best,
Jack