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

Source/core/rendering/FlowThreadController.cpp

Index: Source/core/rendering/FlowThreadController.cpp
diff --git a/Source/core/rendering/FlowThreadController.cpp b/Source/core/rendering/FlowThreadController.cpp
index fed055926cc60ed3a83a7a79564c327aacdfe34b..7ba712ba79a81694f8ad494321a8363754abc62a 100644
--- a/Source/core/rendering/FlowThreadController.cpp
+++ b/Source/core/rendering/FlowThreadController.cpp
@@ -116,7 +116,7 @@ void FlowThreadController::registerNamedFlowContentNode(Node* contentNode, Rende
 void FlowThreadController::unregisterNamedFlowContentNode(Node* contentNode)
 {
     ASSERT(contentNode && contentNode->isElementNode());
-    HashMap<Node*, RenderNamedFlowThread*>::iterator it = m_mapNamedFlowContentNodes.find(contentNode);
+    HashMap<const Node*, RenderNamedFlowThread*>::iterator it = m_mapNamedFlowContentNodes.find(contentNode);
     ASSERT(it != m_mapNamedFlowContentNodes.end());
     ASSERT(it->value);
     ASSERT(it->value->hasContentNode(contentNode));
@@ -225,6 +225,11 @@ void FlowThreadController::updateFlowThreadsIntoConstrainedPhase()
     }
 }
 
+bool FlowThreadController::isContentNodeRegisteredWithAnyNamedFlow(const Node* contentNode) const
+{
+    return m_mapNamedFlowContentNodes.contains(contentNode);
+}
+
 #ifndef NDEBUG
 bool FlowThreadController::isAutoLogicalHeightRegionsCountConsistent() const
 {