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..c2c6094bdd9023585cae35b1292f5d1492863654 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 computeRectForRepaint(const RenderLayerModelObject* repaintContainer, LayoutRect&) const;

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

These 2 functions are really confusing... Can we come up with names that don't
force me to read the comments to know what they do?

It doesn't seem like this function is really computing the rect for repaint.
It's mapping a provided rect to a coordinate space. Is the rect passed in
already clipped?

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

The function is agnostic to the rect's purpose. It's just a dirty rect. Agree
about naming. Changed.
Seems better?

+
+    // 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;