REGRESSION: cnn.com will continue to reveal 1 px of overhang after rubber-banding 
at the top
https://bugs.webkit.org/show_bug.cgi?id=126054

Reviewed by Simon Fraser.

This regression was caused by http://trac.webkit.org/changeset/160791 It turns out 
that the line of code I removed was not always a no-op. In some instances, like on 
cnn.com, it would ensure that our final scroll position after a rubber-band was 
not something within the overhang area. It was still wrong in its assumption that 
rubber-band is always bouncing back the spot it originated from. So this patch 
continues to ignore the rubber-bands origin, and instead finds the nearest point 
that is not in the overhang area, and scrolls to that point instead of the origin.

* page/scrolling/mac/ScrollingTreeScrollingNodeMac.h:
* page/scrolling/mac/ScrollingTreeScrollingNodeMac.mm:
(WebCore::ScrollingTreeScrollingNodeMac::adjustScrollPositionToBoundsIfNecessary):
* platform/mac/ScrollAnimatorMac.h:
* platform/mac/ScrollAnimatorMac.mm:
(WebCore::ScrollAnimatorMac::adjustScrollPositionToBoundsIfNecessary):
* platform/mac/ScrollElasticityController.h:
* platform/mac/ScrollElasticityController.mm:
(WebCore::ScrollElasticityController::snapRubberBandTimerFired):



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@160898 268f45cc-cd09-0410-ab3c-d52691b4dbfc