Allow proper highlighting on universal overflow scroll.

Source/core/rendering/compositing/CompositedLayerMapping.h

Index: Source/core/rendering/compositing/CompositedLayerMapping.h
diff --git a/Source/core/rendering/compositing/CompositedLayerMapping.h b/Source/core/rendering/compositing/CompositedLayerMapping.h
index 62873b7a8d8ea465acc5c312d7805e3da56355e9..f6403e1a57c1fdb6ee870473d5d3b76e891305e1 100644
--- a/Source/core/rendering/compositing/CompositedLayerMapping.h
+++ b/Source/core/rendering/compositing/CompositedLayerMapping.h
@@ -206,6 +206,8 @@ public:
     // If there is a squashed layer painting into this CLM that is an ancestor of the given RenderObject, return it. Otherwise return 0.
     const GraphicsLayerPaintInfo* containingSquashedLayer(const RenderObject*);
 
+    void updateScrollingContentsForSelectionGaps();
+
 private:
     static const GraphicsLayerPaintInfo* containingSquashedLayer(const RenderObject*,  const Vector<GraphicsLayerPaintInfo>& layers);
 
@@ -398,6 +400,7 @@ private:
     bool m_backgroundLayerPaintsFixedRootBackground : 1;
     bool m_needToUpdateGraphicsLayer : 1;
     bool m_needToUpdateGraphicsLayerOfAllDecendants : 1;
+    bool m_scrollingContentsAreEmpty : 1;
 };
 
 } // namespace WebCore