Fix const correctness of containerForRepaint

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 ab372bf195cfadbd4ac0c6221ad7bfa2efc0c6e4..f09c05ceff67132807fa3ce655805e64326cabee 100644
--- a/Source/core/rendering/RenderLayerScrollableArea.cpp
+++ b/Source/core/rendering/RenderLayerScrollableArea.cpp
@@ -380,7 +380,7 @@ void RenderLayerScrollableArea::setScrollOffset(const IntPoint& newScrollOffset)
         updateCompositingLayersAfterScroll();
     }
 
-    RenderLayerModelObject* repaintContainer = box().containerForRepaint();
+    const RenderLayerModelObject* repaintContainer = box().containerForRepaint();
     // The caret rect needs to be invalidated after scrolling
     frame->selection().setCaretRectNeedsUpdate();