Allow proper highlighting on universal overflow scroll.

Source/core/rendering/RenderLayer.cpp

Index: Source/core/rendering/RenderLayer.cpp
diff --git a/Source/core/rendering/RenderLayer.cpp b/Source/core/rendering/RenderLayer.cpp
index 7f7c72fa218bc69f6565bb0e58aa426f1bb3ca60..5a8846ce4a37fbbc3859fa95f85ebacdb56d134f 100644
--- a/Source/core/rendering/RenderLayer.cpp
+++ b/Source/core/rendering/RenderLayer.cpp
@@ -3216,9 +3216,27 @@ RenderLayer* RenderLayer::hitTestChildLayerColumns(RenderLayer* childLayer, Rend
     return 0;
 }
 
+RenderLayer::PresenceOfBlockSelectionGaps RenderLayer::rendererHasBlockSelectionGaps()
+{
+    if (!renderer()->isRenderBlock())
+        return LayerDoesNotHaveBlockSelectionGaps;
+
+    RenderBlock* renderBlock = toRenderBlock(renderer());
+    LayoutRect gapRects = renderBlock->selectionGapRectsForRepaint(renderBlock);
+
+    return gapRects.isEmpty() ? LayerDoesNotHaveBlockSelectionGaps : LayerHasBlockSelectionGaps;
+}
+
+void RenderLayer::blockSelectionGapsBoundsChanged()
+{
+    if (needsCompositedScrolling() && hasCompositedLayerMapping())
+        m_compositedLayerMapping->updateScrollingContentsForSelectionGaps();
+}
+
 void RenderLayer::addBlockSelectionGapsBounds(const LayoutRect& bounds)
 {
     m_blockSelectionGapsBounds.unite(enclosingIntRect(bounds));
+    blockSelectionGapsBoundsChanged();
 }
 
 void RenderLayer::clearBlockSelectionGapsBounds()
@@ -3226,6 +3244,7 @@ void RenderLayer::clearBlockSelectionGapsBounds()
     m_blockSelectionGapsBounds = IntRect();
     for (RenderLayer* child = firstChild(); child; child = child->nextSibling())
         child->clearBlockSelectionGapsBounds();
+    blockSelectionGapsBoundsChanged();
 }
 
 void RenderLayer::repaintBlockSelectionGaps()