Allow proper highlighting on universal overflow scroll.

Source/core/rendering/RenderLayer.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 3198 matching lines @@
             }
 
             if (hitLayer)
                 return hitLayer;
         }
     }
 
     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()
 {
     m_blockSelectionGapsBounds = IntRect();
     for (RenderLayer* child = firstChild(); child; child = child->nextSibling())
         child->clearBlockSelectionGapsBounds();
+    blockSelectionGapsBoundsChanged();
 }
 
 void RenderLayer::repaintBlockSelectionGaps()
 {
     for (RenderLayer* child = firstChild(); child; child = child->nextSibling())
         child->repaintBlockSelectionGaps();
 
     if (m_blockSelectionGapsBounds.isEmpty())
         return;
 
@@ skipping 723 matching lines @@
     }
 }
 
 void showLayerTree(const WebCore::RenderObject* renderer)
 {
     if (!renderer)
         return;
     showLayerTree(renderer->enclosingLayer());
 }
 #endif