[CSS Regions] Elements in a region should be assignable to a named flow

Source/core/dom/PseudoElement.h

Index: Source/core/dom/PseudoElement.h
diff --git a/Source/core/dom/PseudoElement.h b/Source/core/dom/PseudoElement.h
index 5750656d0d053fd145270db6cfc726ac80616e93..05757047280f360cae459306561b9f46d44bbc61 100644
--- a/Source/core/dom/PseudoElement.h
+++ b/Source/core/dom/PseudoElement.h
@@ -45,6 +45,10 @@ public:
     virtual void attach(const AttachContext& = AttachContext()) OVERRIDE;
     virtual bool rendererIsNeeded(const NodeRenderingContext&) OVERRIDE;
 
+    // As per http://dev.w3.org/csswg/css3-regions/#flow-into, pseudo-elements such as ::first-line, ::first-letter, ::before or ::after
+    // cannot be directly collected into a named flow.
+    virtual bool shouldMoveToFlowThread(RenderStyle*) const OVERRIDE { return false; }
+
     virtual bool canStartSelection() const OVERRIDE { return false; }
     virtual bool canContainRangeEndPoint() const OVERRIDE { return false; }