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 734d8aa8e068f8ab94ece0e29d23f08f5f299f83..a9a38a61d5e4cdb76a837558a448b672a8746006 100644
--- a/Source/core/rendering/RenderLayer.cpp
+++ b/Source/core/rendering/RenderLayer.cpp
@@ -3196,9 +3196,27 @@ RenderLayer* RenderLayer::hitTestChildLayerColumns(RenderLayer* childLayer, Rend
     return 0;
 }
 
+IntRect RenderLayer::blockSelectionGapsBounds()
+{
+    if (!renderer()->isRenderBlock())
+        return IntRect();
+
+    RenderBlock* renderBlock = toRenderBlock(renderer());
+    LayoutRect gapRects = renderBlock->selectionGapRectsForRepaint(renderBlock);
+
+    return static_cast<IntRect>(gapRects);

[Ian Vollick, 2014/06/03 17:11:47]

Please be explicit about this conversion. Eg, use pixelSnappedIntRect

+}
+
+void RenderLayer::blockSelectionGapsBoundsChanged()
+{
+    if (needsCompositedScrolling() && hasCompositedLayerMapping())
+        m_compositedLayerMapping->updateScrollingContentsForSelectionGaps(blockSelectionGapsBounds());
+}
+
 void RenderLayer::addBlockSelectionGapsBounds(const LayoutRect& bounds)
 {
     m_blockSelectionGapsBounds.unite(enclosingIntRect(bounds));
+    blockSelectionGapsBoundsChanged();
 }
 
 void RenderLayer::clearBlockSelectionGapsBounds()
@@ -3206,6 +3224,7 @@ void RenderLayer::clearBlockSelectionGapsBounds()
     m_blockSelectionGapsBounds = IntRect();
     for (RenderLayer* child = firstChild(); child; child = child->nextSibling())
         child->clearBlockSelectionGapsBounds();
+    blockSelectionGapsBoundsChanged();
 }
 
 void RenderLayer::repaintBlockSelectionGaps()