I can confirm that I've gotten crash exactly the same as OP before the ANGLE patch. After the patch, I can no longer produce the crash, but get an alert instead warning about the size of the private variable pad.
Bug 1773874 Comment 25 Edit History
Note: The actual edited comment in the bug view page will always show the original commenter’s name and original timestamp.
I can confirm that I've gotten crash exactly the same as OP before the ANGLE patch. After the patch, I can no longer produce the crash, but get an `alert` instead warning about the size of the private variable `pad` from the OP's `poc.html`.