bug#41200: Displaying a tooltip with x-show-tip gets very slow as more faces are defined

[Juri Linkov]

>>>> I think the problem is that tab-line is declared a basic face, but its
>>>> defface form is not in faces.el.
>>>
>>> Ah, good catch.  Current there's a defface for tab-bar in lisp/tab-bar, and 
>>> since that's preloaded it works, but the defface for tab-line is in 
>>> lisp/tab-line.el and so isn't preloaded.
>>> Should I move both to faces.el?
>>>
>> Yes, I think so.
>
> Thanks.  I will ask Juri to confirm before moving them, because I realize now 
> that they have a custom group.
> Juri (CC'd; hi Juri!), was there a reason to make tab-bar and tab-line basic 
> faces?  I see they are both in their own files and groups, instead of being 
> in faces.el.

Actually, no reason other than consistency of faces belonging to the
same file where they are used.  But if it will fix the technical problem,
please move them to faces.el, especially given the fact that their
counterpart tool-bar face is already defined in faces.el.