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.
<rdar://problem/6118969>
Created attachment 22613 [details] patch
Comment on attachment 22613 [details] patch Fabulous.
thanks Eric ! fixed in r35532