bug#39649: 27.0.60; tab-line doesn't scroll

[Juri Linkov]

> Seems to fix the issue in a specific situation, viz. after I select a
> tab manually with the mouse. However, when selecting a buffer that is
> already visible in the tab-line the tab-line still might get scrolled
> or if I just scroll the tab-line and change to a non-visible buffer
> the tab-line doesn't get scrolled. I'm a bit interested in knowing the
> reasoning to not always scroll the tab-line.

While you're manually scrolling the tab-line using the mouse wheel
or clicking on arrow buttons, auto-scrolling should be disabled
because it should not bring the current tab back into view immediately
on every step of manual scrolling.  Just imagine that you clicked
on the arrow button to scroll, but it has no effect because auto-scrolling
immediately moved the tab-line back to its original state.
This is why auto-scrolling should be disabled during manual scrolling.

Now the question: how to detect the moment when you stop manually
scrolling?  How would you indicate that manual scrolling is finished,
and it's time to enable auto-scrolling to bring the currently selected tab
back into view?  I have no idea.