Store repaint rects in the coordinate space of their backing GraphicsLayer.

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 a2c44542a986d305b3d9e0d8cf6f3634ab3d419e..6eef86a36bd38bbcd13a9c700d40f9a08784613e 100644
--- a/Source/core/rendering/RenderLayer.h
+++ b/Source/core/rendering/RenderLayer.h
@@ -351,6 +351,12 @@ public:
     RenderLayer* scrollParent() const;
     RenderLayer* clipParent() const;
 
+    // Adjusts the given rect to the coordinate space of the repaint container's GraphicsLayer backing.
+    void adjustRectToRepaintBackingCoords(const RenderLayerModelObject* repaintContainer, LayoutRect&) const;
+
+    // Computes the bounding repaint rect for this layer, in the coordinate space of the repaint container's GraphicsLayer backing.
+    LayoutRect computeRepaintRect(const RenderLayerModelObject* repaintContainer) const;
+
     bool needsCompositingLayersRebuiltForClip(const RenderStyle* oldStyle, const RenderStyle* newStyle) const;
     bool needsCompositingLayersRebuiltForOverflow(const RenderStyle* oldStyle, const RenderStyle* newStyle) const;
     bool needsCompositingLayersRebuiltForFilters(const RenderStyle* oldStyle, const RenderStyle* newStyle) const;