Refactor root element background painting

Source/core/layout/LayoutBox.h

Index: Source/core/layout/LayoutBox.h
diff --git a/Source/core/layout/LayoutBox.h b/Source/core/layout/LayoutBox.h
index 6e83511d3d3fff7b20d96cecb002bf14e111c9d5..1d8c2f7ef1c1da5612a1a911952c0f187395bfee 100644
--- a/Source/core/layout/LayoutBox.h
+++ b/Source/core/layout/LayoutBox.h
@@ -772,10 +772,11 @@ protected:
 
     virtual bool hasNonCompositedScrollbars() const override final;
 
+    bool mustInvalidateFillLayersPaintOnWidthChange(const FillLayer&) const;
+
 private:
     bool mustInvalidateBackgroundOrBorderPaintOnHeightChange() const;
     bool mustInvalidateBackgroundOrBorderPaintOnWidthChange() const;
-    inline bool mustInvalidateFillLayersPaintOnWidthChange(const FillLayer&) const;
 
     void invalidatePaintRectClippedByOldAndNewBounds(const LayoutBoxModelObject& paintInvalidationContainer, const LayoutRect&, const LayoutRect& oldBounds, const LayoutRect& newBounds);
 
@@ -786,7 +787,7 @@ private:
     LayoutUnit shrinkToFitLogicalWidth(LayoutUnit availableLogicalWidth, LayoutUnit bordersPlusPadding) const;
 
     // Returns true if we queued up a paint invalidation.
-    bool paintInvalidationLayerRectsForImage(WrappedImagePtr, const FillLayer&, bool drawingBackground);
+    bool invalidatePaintOfLayerRectsForImage(WrappedImagePtr, const FillLayer&, bool drawingBackground);
 
     bool skipContainingBlockForPercentHeightCalculation(const LayoutBox* containingBlock) const;