bug#46827: Broken initial size of GTK3 frame

[Juri Linkov]

>> Actually, now there is only one successful scenario: it doesn't flash
>> with sit-for, but still flashes with a message.
>
> Does "now" mean after my most recent commit?

I don't know whether it affected since anyway sit-for can be used for
workaround as a test without flash.

> Didn't you earlier say that all this happens in a maximized frame?  The
> sizes above seem to contradict that.

For testing, I tried in an unmaximized frame, but the problem is the same.

> In either case, someone requests to enlarge and shrink the tab bar by
> two pixels which contradicts your earlier "and the tab bar is not
> resized".

There are no visible resizes.

> So who wants to do that to the tab bar and why?

I don't know who wants to resize by two pixels.

> And who wants to set the window configuration here and why?

I added a breakpoint in set-window-configuration, and it's called from
tab-bar-select-tab in Gnus.

In total there are 4 tab switches with 4 calls of set-window-configuration.
But after removing gnus-remove-some-windows, when set-window-configuration
is not called at all, there are still the same flashes.