Overlay scrollbars must respect ancestor clip

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 5871a502fb9036b79b1d2b1bb0f9a6679b22da5e..cb4da7b53cc9f099162b49a46f50f08f7e6582ec 100644
--- a/Source/core/rendering/RenderLayer.h
+++ b/Source/core/rendering/RenderLayer.h
@@ -553,6 +553,8 @@ public:
 
     void didUpdateNeedsCompositedScrolling();
 
+    bool needsToReparentOverflowControls() const;

[chrishtr, 2014/07/25 21:06:15]

On reflection, this is weird to put on RenderLayer, since it's specific to
graphics layer hierarchies.
Instead let's put it on RenderLayerCompositor?

Also please add a comment as this concept is confusing.

[Ian Vollick, 2014/07/26 01:54:57]

Yeah, now that you mention it, I agree that RenderLayer isn't a good home for
this fn. I thought that it fit well in CompositedLayerMapping, though, so I've
stuck it there and added an explanatory comment. Please let me know if you think
that this still doesn't make sense in the CLM.

+
 private:
     // Bounding box in the coordinates of this layer.
     LayoutRect logicalBoundingBox() const;