Allow proper highlighting on universal overflow scroll.

Source/core/rendering/RenderLayerScrollableArea.cpp

Index: Source/core/rendering/RenderLayerScrollableArea.cpp
diff --git a/Source/core/rendering/RenderLayerScrollableArea.cpp b/Source/core/rendering/RenderLayerScrollableArea.cpp
index 911dd1a8694f8f125465d3abc30349da4986d9c7..4ac94a889a918a5629968ad4c9a7990ee4d9d2e8 100644
--- a/Source/core/rendering/RenderLayerScrollableArea.cpp
+++ b/Source/core/rendering/RenderLayerScrollableArea.cpp
@@ -399,7 +399,6 @@ void RenderLayerScrollableArea::setScrollOffset(const IntPoint& newScrollOffset)
         bool onlyScrolledCompositedLayers = scrollsOverflow()
             && !layer()->hasVisibleNonLayerContent()
             && !layer()->hasNonCompositedChild()
-            && !layer()->hasBlockSelectionGapBounds()

[hartmanng, 2014/06/13 14:51:38]

This is no longer needed, because the block selection gaps bounds will now never
have to repaint on scroll. They will either be part of the scrolling contents
layer, or part of the block selection layer, but never part of the background.

This removal should also fix the scroll-update chicken-egg problems, so this
patch shouldn't be blocked anymore.

[hartmanng, 2014/06/13 16:43:56]

After talking with Ian offline, I think I was wrong about this. I misunderstood
what was going on here. This bool is only relevant if we're _not_ using
composited scrolling, so my patch shouldn't affect the behaviour here.

             && !box().isMarquee();
 
         if (usesCompositedScrolling() || onlyScrolledCompositedLayers)