Refactor root element background painting

Source/core/layout/LayoutView.h

Index: Source/core/layout/LayoutView.h
diff --git a/Source/core/layout/LayoutView.h b/Source/core/layout/LayoutView.h
index 82fb7698f4085283687d89f2fd2e68f7ca1d4236..4dac05126b8593ab1c463773926ace02f0dc5030 100644
--- a/Source/core/layout/LayoutView.h
+++ b/Source/core/layout/LayoutView.h
@@ -173,7 +173,21 @@ public:
     void popLayoutState() { ASSERT(m_layoutState); m_layoutState = m_layoutState->next(); }
     virtual void invalidateTreeIfNeeded(PaintInvalidationState&) override final;
 
+protected:
+    virtual void styleDidChange(StyleDifference, const ComputedStyle* oldStyle) override;
+    virtual PaintInvalidationReason paintInvalidationReason(const LayoutBoxModelObject& paintInvalidationContainer,
+        const LayoutRect& oldBounds, const LayoutPoint& oldLocation,
+        const LayoutRect& newBounds, const LayoutPoint& newLocation) const override;
+    virtual PaintInvalidationReason invalidatePaintIfNeeded(PaintInvalidationState&, const LayoutBoxModelObject& newPaintInvalidationContainer) override;
+
 private:
+    struct BackgroundPositioning {
+        TransformationMatrix transform;
+        LayoutSize borderBoxSize;
+        LayoutRect paddingBoxRect;
+        LayoutRect contentBoxRect;
+    };
+
     virtual void mapLocalToContainer(const LayoutBoxModelObject* paintInvalidationContainer, TransformState&, MapCoordinatesFlags = ApplyContainerFlip, bool* wasFixed = 0, const PaintInvalidationState* = 0) const override;
     virtual const LayoutObject* pushMappingToContainer(const LayoutBoxModelObject* ancestorToStopAt, LayoutGeometryMap&) const override;
     virtual void mapAbsoluteToLocalPoint(MapCoordinatesFlags, TransformState&) const override;
@@ -188,11 +202,11 @@ private:
 
     bool shouldUsePrintingLayout() const;
 
-    LayoutObject* backgroundLayoutObject() const;
-
     int viewLogicalWidthForBoxSizing() const;
     int viewLogicalHeightForBoxSizing() const;
 
+    void getBackgroundPositioningFromDocumentElement(BackgroundPositioning&) const;
+
     FrameView* m_frameView;
 
     LayoutObject* m_selectionStart;
@@ -212,6 +226,8 @@ private:
 
     unsigned m_hitTestCount;
 
+    BackgroundPositioning m_previousRootBackgroundPositioning;
+
     OwnPtrWillBePersistent<PendingSelection> m_pendingSelection;
 };