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

[Clément Pit-Claudel]

On 12/05/2020 11.12, martin rudalics wrote:
>>> Please try with 'tooltip-reuse-hidden-frame' non-nil (there's nothing we
>>> can do about a session's first tooltip appearance, though).
>>
>> I'm not seeing a difference here.  I used this code to test:
> 
> Looks like a devastating bug in the GTK builds.  Can you try with the
> attached patch?
> 
> Thanks, martin

Indeed, with tooltip-reuse-hidden-frame t and your patch, creating a tooltip is 
instantaneous (after the first tooltip is created)
The docstring suggests that with this option, results won't always be correct.  
Is there a chance that we could rebuild the frame when needed and then make 
that option the default?