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

Source/core/rendering/CompositedLayerMapping.cpp

Index: Source/core/rendering/CompositedLayerMapping.cpp
diff --git a/Source/core/rendering/CompositedLayerMapping.cpp b/Source/core/rendering/CompositedLayerMapping.cpp
index 63662d10f71b14b21df2ba1142867eb3d1e74459..b860ffbefb2865019bdccf60a46970e0acae101b 100644
--- a/Source/core/rendering/CompositedLayerMapping.cpp
+++ b/Source/core/rendering/CompositedLayerMapping.cpp
@@ -366,7 +366,7 @@ void CompositedLayerMapping::updateCompositedBounds()
             clippingBounds = view->unscaledDocumentRect();
 
         if (m_owningLayer != rootLayer)
-            clippingBounds.intersect(m_owningLayer->clipper().backgroundClipRect(ClipRectsContext(rootLayer, 0, AbsoluteClipRects)).rect()); // FIXME: Incorrect for CSS regions.
+            clippingBounds.intersect(m_owningLayer->clipper().backgroundClipRect(ClipRectsContext(rootLayer, AbsoluteClipRects)).rect());
 
         LayoutPoint delta;
         m_owningLayer->convertToLayerCoords(rootLayer, delta);
@@ -539,10 +539,10 @@ static IntRect clipBox(RenderBox* renderer)
 {
     LayoutRect result = PaintInfo::infiniteRect();
     if (renderer->hasOverflowClip())
-        result = renderer->overflowClipRect(LayoutPoint(), 0); // FIXME: Incorrect for CSS regions.
+        result = renderer->overflowClipRect(LayoutPoint());
 
     if (renderer->hasClip())
-        result.intersect(renderer->clipRect(LayoutPoint(), 0)); // FIXME: Incorrect for CSS regions.
+        result.intersect(renderer->clipRect(LayoutPoint()));
 
     return pixelSnappedIntRect(result);
 }
@@ -641,7 +641,7 @@ void CompositedLayerMapping::updateGraphicsLayerGeometry()
         // Call calculateRects to get the backgroundRect which is what is used to clip the contents of this
         // layer. Note that we call it with temporaryClipRects = true because normally when computing clip rects
         // for a compositing layer, rootLayer is the layer itself.
-        ClipRectsContext clipRectsContext(compAncestor, 0, TemporaryClipRects, IgnoreOverlayScrollbarSize, IgnoreOverflowClip);
+        ClipRectsContext clipRectsContext(compAncestor, TemporaryClipRects, IgnoreOverlayScrollbarSize, IgnoreOverflowClip);
         IntRect parentClipRect = pixelSnappedIntRect(m_owningLayer->clipper().backgroundClipRect(clipRectsContext).rect()); // FIXME: Incorrect for CSS regions.
         ASSERT(parentClipRect != PaintInfo::infiniteRect());
         m_ancestorClippingLayer->setPosition(FloatPoint(parentClipRect.location() - graphicsLayerParentLocation));
@@ -1478,9 +1478,6 @@ bool CompositedLayerMapping::isSimpleContainerCompositingLayer() const
     if (paintsBoxDecorations() || paintsChildren())
         return false;
 
-    if (renderObject->isRenderRegion())
-        return false;
-
     if (renderObject->node() && renderObject->node()->isDocumentNode()) {
         // Look to see if the root object has a non-simple background
         RenderObject* rootObject = renderObject->document().documentElement() ? renderObject->document().documentElement()->renderer() : 0;
@@ -1876,7 +1873,6 @@ void CompositedLayerMapping::doPaintTask(GraphicsLayerPaintInfo& paintInfo, Grap
 #endif
 
     if (paintInfo.renderLayer->compositingState() != PaintsIntoGroupedBacking) {
-        // FIXME: GraphicsLayers need a way to split for RenderRegions.
         LayerPaintingInfo paintingInfo(paintInfo.renderLayer, dirtyRect, PaintBehaviorNormal, m_subpixelAccumulation);
         paintInfo.renderLayer->paintLayerContents(context, paintingInfo, paintFlags);