bug#37667: 27.0.50; Tab Bar display problems with more than 5 tabs

[Juri Linkov]

>> >  . Display one arrow on the left and another on the right, and decide
>> >    whether or not to display the right one in display_mode_line,
>> >    depending on whether you hit (last_visible_x - arrow_width) while
>> >    producing glyphs.
>> 
>> Do you mean displaying the arrow on the right using fringe?
>
> No, I meant displaying them like you do now, just move the right arrow
> to the right of the last visible tab.

This requires a function to find the last visible tab.
Maybe it would be possible to reuse the same new function
that will detect if the current tab is visible.

>> > The first one sounds the easiest to me.
>> 
>> The first one is easy to implement, but it can't do auto-scrolling,
>> i.e. when the current tab becomes invisible, automattically reduce
>> the number of tabs in front of it to make it visible.
>
> Is that such a serious problem?  Browsers don't auto-scroll.

Chromium doesn't auto-scroll because it reduces every tab width
to fit all tabs to the tab bar, so there is no scrolling.
But Firefox auto-scrolls the tab bar to the current tab.