Repaint when background switches painting from/to scrolling contents layer.

third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.h

 /*
  * Copyright (C) 2009, 2010, 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 69 matching lines @@
     WTF_MAKE_NONCOPYABLE(CompositedLayerMapping); USING_FAST_MALLOC(CompositedLayerMapping);
 public:
     explicit CompositedLayerMapping(PaintLayer&);
     ~CompositedLayerMapping() override;
 
     PaintLayer& owningLayer() const { return m_owningLayer; }
 
     bool updateGraphicsLayerConfiguration();
     void updateGraphicsLayerGeometry(const PaintLayer* compositingContainer, const PaintLayer* compositingStackingContext, Vector<PaintLayer*>& layersNeedingPaintInvalidation);
 
+    // Update whether background paints onto scrolling contents layer.
+    void updateBackgroundPaintingLayer();
+
     // Update whether layer needs blending.
     void updateContentsOpaque();
 
     GraphicsLayer* mainGraphicsLayer() const { return m_graphicsLayer.get(); }
 
     // Layer to clip children
     bool hasClippingLayer() const { return m_childContainmentLayer.get(); }
     GraphicsLayer* clippingLayer() const { return m_childContainmentLayer.get(); }
 
     // Layer to get clipped by ancestor
@@ skipping 116 matching lines @@
     void updateScrollingBlockSelection();
 
     void adjustForCompositedScrolling(const GraphicsLayer*, IntSize& offset) const;
 
     // Returns true for layers with scrollable overflow which have a background
     // that can be painted into the composited scrolling contents layer (i.e.
     // the background can scroll with the content). When the background is also
     // opaque this allows us to composite the scroller even on low DPI as we can
     // draw with subpixel anti-aliasing.
     bool shouldPaintBackgroundOntoScrollingContentsLayer() const;
+    bool backgroundPaintsOntoScrollingContentsLayer() { return m_backgroundPaintsOntoScrollingContentsLayer; }
 
 private:
     IntRect recomputeInterestRect(const GraphicsLayer*) const;
     static bool interestRectChangedEnoughToRepaint(const IntRect& previousInterestRect, const IntRect& newInterestRect, const IntSize& layerSize);
 
     static const GraphicsLayerPaintInfo* containingSquashedLayer(const LayoutObject*,  const Vector<GraphicsLayerPaintInfo>& layers, unsigned maxSquashedLayerIndex);
 
     // Paints the scrollbar part associated with the given graphics layer into the given context.
     void paintScrollableArea(const GraphicsLayer*, GraphicsContext&, const IntRect& interestRect) const;
     // Returns whether the given layer is part of the scrollable area, if any, associated with this mapping.
@@ skipping 218 matching lines @@
     DoubleSize m_scrollingContentsOffset;
 
     unsigned m_contentOffsetInCompositingLayerDirty : 1;
 
     unsigned m_pendingUpdateScope : 2;
     unsigned m_isMainFrameLayoutViewLayer : 1;
 
     unsigned m_backgroundLayerPaintsFixedRootBackground : 1;
     unsigned m_scrollingContentsAreEmpty : 1;
 
+    // Keep track of whether the background is painted onto the scrolling contents layer for invalidations.
+    unsigned m_backgroundPaintsOntoScrollingContentsLayer : 1;
+
     friend class CompositedLayerMappingTest;
 };
 
 } // namespace blink
 
 #endif // CompositedLayerMapping_h