*** DO NOT LAND *** Attempt to understand Regions complexity

Source/core/rendering/RenderLayerCompositor.cpp

Index: Source/core/rendering/RenderLayerCompositor.cpp
diff --git a/Source/core/rendering/RenderLayerCompositor.cpp b/Source/core/rendering/RenderLayerCompositor.cpp
index b86537ee32d7dc01985c884de4c16f90795b893c..4b6ec1e5f4637e5c30162baea0a3caf3bf78d70a 100644
--- a/Source/core/rendering/RenderLayerCompositor.cpp
+++ b/Source/core/rendering/RenderLayerCompositor.cpp
@@ -761,7 +761,7 @@ void RenderLayerCompositor::addToOverlapMap(OverlapMap& overlapMap, RenderLayer*
         boundsComputed = true;
     }
 
-    IntRect clipRect = pixelSnappedIntRect(layer->clipper().backgroundClipRect(ClipRectsContext(rootRenderLayer(), 0, AbsoluteClipRects)).rect()); // FIXME: Incorrect for CSS regions.
+    IntRect clipRect = pixelSnappedIntRect(layer->clipper().backgroundClipRect(ClipRectsContext(rootRenderLayer(), AbsoluteClipRects)).rect()); // FIXME: Incorrect for CSS regions.
     clipRect.intersect(layerBounds);
     overlapMap.add(layer, clipRect);
 }
@@ -1673,7 +1673,7 @@ bool RenderLayerCompositor::canBeComposited(const RenderLayer* layer) const
 {
     // FIXME: We disable accelerated compositing for elements in a RenderFlowThread as it doesn't work properly.
     // See http://webkit.org/b/84900 to re-enable it.
-    return m_hasAcceleratedCompositing && layer->isSelfPaintingLayer() && layer->renderer()->flowThreadState() == RenderObject::NotInsideFlowThread;
+    return m_hasAcceleratedCompositing && layer->isSelfPaintingLayer();
 }
 
 CompositingReasons RenderLayerCompositor::directReasonsForCompositing(const RenderLayer* layer) const
@@ -1753,7 +1753,7 @@ bool RenderLayerCompositor::clippedByAncestor(const RenderLayer* layer) const
     if (!computeClipRoot || computeClipRoot == layer)
         return false;
 
-    return layer->clipper().backgroundClipRect(ClipRectsContext(computeClipRoot, 0, TemporaryClipRects)).rect() != PaintInfo::infiniteRect(); // FIXME: Incorrect for CSS regions.
+    return layer->clipper().backgroundClipRect(ClipRectsContext(computeClipRoot, TemporaryClipRects)).rect() != PaintInfo::infiniteRect();
 }
 
 // Return true if the given layer is a stacking context and has compositing child