Revert 140571

Revert 140571
> https://bugs.webkit.org/show_bug.cgi?id=107628
> Sometimes scroll position is jerky during rubber-band, affects nytimes.com
> -and corresponding-
> <rdar://problem/12679549>
> 
> Reviewed by Simon Fraser.
> 
> The basic problem here is that isRubberBandInProgress() was only implemented for 
> main thread scrolling. So when we were actually scrolling on the scrolling thread, 
> that function would always return false regardless.
> 
> New ScrollableArea virtual function isRubberBandInProgress() will allow us to ask 
> the ScrollingCoordinator when the scrolling thread is scrolling, or the 
> ScrollAnimator otherwise.
> * page/FrameView.cpp:
> (WebCore::FrameView::isRubberBandInProgress):
> * page/FrameView.h:
> (FrameView):
> * platform/ScrollableArea.h:
> (WebCore::ScrollableArea::isRubberBandInProgress):
> 
> New ScrollingCoordinator function isRubberBandInProgress() always returns false 
> for non-Mac ports, and is overridden in ScrollingCoordinatorMac to consult the 
> ScrollingTree.
> * page/scrolling/ScrollingCoordinator.h:
> (WebCore::ScrollingCoordinator::isRubberBandInProgress):
> * page/scrolling/mac/ScrollingCoordinatorMac.h:
> (ScrollingCoordinatorMac):
> * page/scrolling/mac/ScrollingCoordinatorMac.mm:
> (WebCore::ScrollingCoordinatorMac::isRubberBandInProgress):
> 
> New variable m_mainFrameIsRubberBanding keeps track of whether there is currently 
> a rubber-band happening on the scrolling thread.
> * page/scrolling/ScrollingTree.cpp:
> (WebCore::ScrollingTree::ScrollingTree):
> (WebCore::ScrollingTree::isRubberBandInProgress):
> (WebCore::ScrollingTree::setMainFrameIsRubberBanding):
> * page/scrolling/ScrollingTree.h:
> (ScrollingTree):
> (WebCore::ScrollingTree::rootNode):
> 
> Call setMainFrameIsRubberBanding() whenever the stretchAmount is calculated and 
> whenever we stop the rubber-band timer.
> * page/scrolling/mac/ScrollingTreeScrollingNodeMac.mm:
> (WebCore::ScrollingTreeScrollingNodeMac::stretchAmount):
> (WebCore::ScrollingTreeScrollingNodeMac::stopSnapRubberbandTimer):
> 
> Consult FrameView for isRubberBandInProgress().
> * platform/ScrollView.cpp:
> (WebCore::ScrollView::updateScrollbars):
> 
> 

TBR=jamesr@chromium.org
BUG=173009
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=143053