Get rid of a lot of special code for RenderFlowThread invalidation.

Source/core/rendering/RenderFlowThread.h

Index: Source/core/rendering/RenderFlowThread.h
diff --git a/Source/core/rendering/RenderFlowThread.h b/Source/core/rendering/RenderFlowThread.h
index 74a6b9cb50c34fa38658469ba0c5b208af1935e2..b77c57c3dc5a0582520343f10a43c90ad7ffd042 100644
--- a/Source/core/rendering/RenderFlowThread.h
+++ b/Source/core/rendering/RenderFlowThread.h
@@ -61,6 +61,8 @@ public:
     virtual bool isRenderMultiColumnFlowThread() const { return false; }
     virtual bool isRenderPagedFlowThread() const { return false; }
 
+    virtual bool supportsPaintInvalidationStateCachedOffsets() const override { return false; }
+
     virtual void layout() override;
 
     // Always create a RenderLayer for the RenderFlowThread so that we
@@ -82,7 +84,7 @@ public:
     void invalidateRegions();
     bool hasValidRegionInfo() const { return !m_regionsInvalidated && !m_multiColumnSetList.isEmpty(); }
 
-    void paintInvalidationRectangleInRegions(const LayoutRect&) const;
+    virtual void mapRectToPaintInvalidationBacking(const RenderLayerModelObject* paintInvalidationContainer, LayoutRect&, const PaintInvalidationState*) const override;
 
     LayoutUnit pageLogicalHeightForOffset(LayoutUnit);
     LayoutUnit pageRemainingLogicalHeightForOffset(LayoutUnit, PageBoundaryRule = IncludePageBoundary);
@@ -102,7 +104,7 @@ public:
     bool pageLogicalSizeChanged() const { return m_pageLogicalSizeChanged; }
 
     void collectLayerFragments(LayerFragments&, const LayoutRect& layerBoundingBox, const LayoutRect& dirtyRect);
-    LayoutRect fragmentsBoundingBox(const LayoutRect& layerBoundingBox);
+    LayoutRect fragmentsBoundingBox(const LayoutRect& layerBoundingBox) const;
 
     LayoutPoint flowThreadPointToVisualPoint(const LayoutPoint& flowThreadPoint) const
     {
@@ -120,7 +122,6 @@ protected:
     virtual const char* renderName() const = 0;
 
     void updateRegionsFlowThreadPortionRect();
-    bool shouldIssuePaintInvalidations(const LayoutRect&) const;
 
     virtual RenderMultiColumnSet* columnSetAtBlockOffset(LayoutUnit) const = 0;