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

Source/core/rendering/FlowThreadController.h

 /*
  * Copyright (C) 2012 Adobe Systems Incorporated. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1. Redistributions of source code must retain the above
  *    copyright notice, this list of conditions and the following
  *    disclaimer.
@@ skipping 48 matching lines @@
     }
 
     RenderNamedFlowThread* ensureRenderFlowThreadWithName(const AtomicString&);
     const RenderNamedFlowThreadList* renderNamedFlowThreadList() const { return m_renderNamedFlowThreadList.get(); }
     bool hasRenderNamedFlowThreads() const { return m_renderNamedFlowThreadList && !m_renderNamedFlowThreadList->isEmpty(); }
     void layoutRenderNamedFlowThreads();
     void styleDidChange();
 
     void registerNamedFlowContentNode(Node*, RenderNamedFlowThread*);
     void unregisterNamedFlowContentNode(Node*);
+    bool isContentNodeRegisteredWithAnyNamedFlow(const Node*) const;
 
     bool hasFlowThreadsWithAutoLogicalHeightRegions() const { return m_flowThreadsWithAutoLogicalHeightRegions; }
     void incrementFlowThreadsWithAutoLogicalHeightRegions() { ++m_flowThreadsWithAutoLogicalHeightRegions; }
     void decrementFlowThreadsWithAutoLogicalHeightRegions() { ASSERT(m_flowThreadsWithAutoLogicalHeightRegions > 0); --m_flowThreadsWithAutoLogicalHeightRegions; }
 
     bool updateFlowThreadsNeedingLayout();
     bool updateFlowThreadsNeedingTwoStepLayout();
     void updateFlowThreadsIntoConstrainedPhase();
 
 #ifndef NDEBUG
     bool isAutoLogicalHeightRegionsCountConsistent() const;
 #endif
 
 protected:
     FlowThreadController(RenderView*);
     void updateFlowThreadsChainIfNecessary();
     void resetFlowThreadsWithAutoHeightRegions();
 
 private:
     RenderView* m_view;
     RenderFlowThread* m_currentRenderFlowThread;
     bool m_isRenderNamedFlowThreadOrderDirty;
     unsigned m_flowThreadsWithAutoLogicalHeightRegions;
     OwnPtr<RenderNamedFlowThreadList> m_renderNamedFlowThreadList;
     // maps a content node to its render flow thread.
-    HashMap<Node*, RenderNamedFlowThread*> m_mapNamedFlowContentNodes;
+    HashMap<const Node*, RenderNamedFlowThread*> m_mapNamedFlowContentNodes;
 };
 
 }
 
 #endif