After adding the auto-scroll by middle-click we should modify the mouse cursor to show the direction of the scroll interactively.
Look at https://bugs.webkit.org/show_bug.cgi?id=16424 to see what feature I'm talking about.
The cursor can be an arrow pointing to the current scroll direction.
Created attachment 22613 [details]
Comment on attachment 22613 [details]
thanks Eric !
fixed in r35532