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

Source/core/rendering/FlowThreadController.h

Index: Source/core/rendering/FlowThreadController.h
diff --git a/Source/core/rendering/FlowThreadController.h b/Source/core/rendering/FlowThreadController.h
index c0b6a1bbdcda1dba993e7973f160b6ec7007cf26..0f014cdb062b061f2540781d5878d59f9f2c9fd1 100644
--- a/Source/core/rendering/FlowThreadController.h
+++ b/Source/core/rendering/FlowThreadController.h
@@ -66,6 +66,7 @@ public:
 
     void registerNamedFlowContentNode(Node*, RenderNamedFlowThread*);
     void unregisterNamedFlowContentNode(Node*);
+    bool isContentNodeRegisteredWithAnyNamedFlow(const Node*) const;
 
     bool hasFlowThreadsWithAutoLogicalHeightRegions() const { return m_flowThreadsWithAutoLogicalHeightRegions; }
     void incrementFlowThreadsWithAutoLogicalHeightRegions() { ++m_flowThreadsWithAutoLogicalHeightRegions; }
@@ -91,7 +92,7 @@ private:
     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;
 };
 
 }