Defer the real work in updateCompositingLayers until it's really needed.

Source/core/rendering/RenderLayer.h

Index: Source/core/rendering/RenderLayer.h
diff --git a/Source/core/rendering/RenderLayer.h b/Source/core/rendering/RenderLayer.h
index d5677d8d99269091e5c089477141c5d580f33f4f..cd200f5bfd631d57d648c315cfb78ef37ab29aac 100644
--- a/Source/core/rendering/RenderLayer.h
+++ b/Source/core/rendering/RenderLayer.h
@@ -193,7 +193,6 @@ public:
     void updateLayerPositionsAfterOverflowScroll();
     void updateLayerPositionsAfterDocumentScroll();
 
-    void positionNewlyCreatedOverflowControls();
 
     bool isPaginated() const { return m_isPaginated; }
     RenderLayer* enclosingPaginationLayer() const { return m_enclosingPaginationLayer; }
@@ -751,6 +750,9 @@ private:
 
     RenderLayer* enclosingTransformedAncestor() const;
 
+    // If IntSize is not given, then we must incur additional overhead to instantiate a RenderGeometryMap
+    // and compute the correct offset ourselves.
+    void positionOverflowControls();
     void positionOverflowControls(const IntSize&);
 
     void updatePagination();