Adjusting relatedTarget can be much faster and more accurate

Once we have O(1) access to shadowRoot, we can:

1) Easily determine whether we even need to walk anything.
2) Use scopes to check whether we need to adjust relatedTarget. See http://dev.w3.org/2006/xbl2/#the-mouseover-and-mouseout-events for more details.
3) Use scope chain to walk more quickly.

I think we already have O(1) access to shadowRoot. Let me rewrite adjust relatedTarget code.

(In reply to comment #1)
> I think we already have O(1) access to shadowRoot. Let me rewrite adjust relatedTarget code.

SVG is still blocking you :(.

Thank you for the info. SVG still looks blocking as you said. :(

(In reply to comment #2)
> (In reply to comment #1)
> > I think we already have O(1) access to shadowRoot. Let me rewrite adjust relatedTarget code.
> 
> SVG is still blocking you :(.

This isn't causing:
http://samples.msdn.microsoft.com/ietestcenter/domevents/mouseleave.relatedTarget.html
and:
http://samples.msdn.microsoft.com/ietestcenter/domevents/mouseenter.ctrlKey.html

is it?

Sorry, http://samples.msdn.microsoft.com/ietestcenter/domevents/mouseenter.relatedTarget.html

Nevermind.  We don't support those two events.  https://bugs.webkit.org/show_bug.cgi?id=18930