[WinCairo] Unreviewed build fix after r144024.

* page/scrolling/ScrollingCoordinator.cpp:
(WebCore::ScrollingCoordinator::scrollLayerForScrollableArea): Handle
case of not using Accelerated Compositing
(WebCore::ScrollingCoordinator::horizontalScrollbarLayerForScrollableArea):
(WebCore::ScrollingCoordinator::verticalScrollbarLayerForScrollableArea): Ditto.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@144799 268f45cc-cd09-0410-ab3c-d52691b4dbfc