Don't rely on values computed as a side effect of paint.

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 f853c269513d06935c90b40684118bb58a9ec078..4b3b8623948366c71cc45588967310b9fcdc0e3c 100644
--- a/Source/core/rendering/RenderLayerScrollableArea.cpp
+++ b/Source/core/rendering/RenderLayerScrollableArea.cpp
@@ -395,8 +395,8 @@ void RenderLayerScrollableArea::setScrollOffset(const IntPoint& newScrollOffset)
         bool onlyScrolledCompositedLayers = scrollsOverflow()
             && !layer()->hasVisibleNonLayerContent()
             && !layer()->hasNonCompositedChild()
-            && !layer()->hasBlockSelectionGapBounds()
-            && !m_box->isMarquee();
+            && !m_box->isMarquee()
+            && layer()->renderer()->selectionRectForRepaint(0, true).isEmpty();

[abarth-chromium, 2014/03/21 15:45:54]

Why not just call selectionRect() ?  That supplies these values for you.

[Ian Vollick, 2014/03/21 17:01:50]

Thanks, that's way better. Done.

 
         if (usesCompositedScrolling() || onlyScrolledCompositedLayers)
             requiresRepaint = false;