XUL:Specs:Scrolling

Current State

• Scroll events are fired, but only if attached using addEventListener.
• nsIScrollbarListener sends callbacks but there is no consumer listening to them
• scrollbox is the only element that has a API to retrieve and adjust the scroll position, yet all elements may be scrollable.

Changes

• Add onscroll event for XUL elements. May be just a matter of adding to the list in nsXULElement::IsEventHandler
• Remove nsIScrollbarListener
• The simplest way to make any element have a scrollable API is to just make nsBoxObject implement nsIScrollBoxObject, and put in the appropriate classinfo changes.