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

Source/core/rendering/RenderBox.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2006, 2007 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 390 matching lines @@
     void dirtyLineBoxes(bool fullLayout);
 
     // For inline replaced elements, this function returns the inline box that owns us.  Enables
     // the replaced RenderObject to quickly determine what line it is contained on and to easily
     // iterate over structures on the line.
     InlineBox* inlineBoxWrapper() const { return m_rareData ? m_rareData->m_inlineBoxWrapper : 0; }
     void setInlineBoxWrapper(InlineBox*);
     void deleteLineBoxWrapper();
 
     virtual LayoutRect clippedOverflowRectForRepaint(const RenderLayerModelObject* repaintContainer) const OVERRIDE;
-    virtual void computeRectForRepaint(const RenderLayerModelObject* repaintContainer, LayoutRect&, bool fixed = false) const OVERRIDE;
+    virtual void adjustRectToRepaintBackingCoords(const RenderLayerModelObject* repaintContainer, LayoutRect&, bool fixed = false) const OVERRIDE;

[leviw_travelin_and_unemployed, 2014/05/29 20:49:00]

We use "map" in other parts of blink to signify transforming between coordinate
systems. How about mapRectToRepaintBacking?

[chrishtr, 2014/05/29 21:06:11]

Done.

     void repaintDuringLayoutIfMoved(const LayoutRect&);
     virtual void repaintOverhangingFloats(bool paintAllDescendants);
 
     virtual LayoutUnit containingBlockLogicalWidthForContent() const OVERRIDE;
     LayoutUnit containingBlockLogicalHeightForContent(AvailableLogicalHeightType) const;
 
     LayoutUnit containingBlockAvailableLineWidth() const;
     LayoutUnit perpendicularContainingBlockLogicalHeight() const;
 
     virtual void updateLogicalWidth();
@@ skipping 352 matching lines @@
         if (UNLIKELY(inlineBoxWrapper() != 0))
             deleteLineBoxWrapper();
     }
 
     ensureRareData().m_inlineBoxWrapper = boxWrapper;
 }
 
 } // namespace WebCore
 
 #endif // RenderBox_h