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

Source/core/rendering/RenderObject.h

Index: Source/core/rendering/RenderObject.h
diff --git a/Source/core/rendering/RenderObject.h b/Source/core/rendering/RenderObject.h
index 77c5e8f8b32d0e1279602cc208430a09ba561a8f..8d7ecf005524a208bfae11ca09687e0627a0c3a9 100644
--- a/Source/core/rendering/RenderObject.h
+++ b/Source/core/rendering/RenderObject.h
@@ -807,8 +807,11 @@ public:
     bool isRepaintContainer() const;
 
     // Returns the repaint rect for this RenderObject in the coordinate space of the composited layer that this RenderObject paints into, or the RenderView if not
-    // composited.
-    LayoutRect computeRepaintRect() const;
+    // composited. If |repaintContainer| is 0, uses containerForRepaint().
+    LayoutRect computeRepaintRect(const RenderLayerModelObject* repaintContainer = 0) const;

[leviw_travelin_and_unemployed, 2014/05/29 18:27:08]

How about a computeRepaintRect that takes no parameters that's inline and calls
the one that takes a parameter with containerForRepaint? I only suggest this
because we want to be very clear that you should never be in this code without a
repaint container.

[chrishtr, 2014/05/29 18:34:11]

Never be in this code without a repaint container? What do you mean?

+
+    // Returns the rect bounds needed to repaint this object, in the coordinate space of the rendering backing of |repaintContainer|
+    LayoutRect boundsRectForRepaint(const RenderLayerModelObject* repaintContainer) const;
 
     // Actually do the repaint of rect r for this object which has been computed in the coordinate space
     // of repaintContainer. If repaintContainer is 0, repaint via the view.
@@ -1077,8 +1080,6 @@ protected:
     virtual void computeSelfHitTestRects(Vector<LayoutRect>&, const LayoutPoint& layerOffset) const { };
 
 private:
-    LayoutRect computeRepaintRectInternal(const RenderLayerModelObject* repaintContainer) const;
-
     RenderBlock* containerForFixedPosition(const RenderLayerModelObject* repaintContainer = 0, bool* repaintContainerSkipped = 0) const;
 
     RenderFlowThread* locateFlowThreadContainingBlock() const;