Make sure to lazyReattach a distributed node if it is already attached

third_party/WebKit/Source/core/html/HTMLSlotElement.h

 /*
  * Copyright (C) 2015 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 43 matching lines @@
     Node* distributedNodePreviousTo(const Node&) const;
 
     void appendAssignedNode(Node&);
 
     void resolveDistributedNodes();
     void appendDistributedNode(Node&);
     void appendDistributedNodesFrom(const HTMLSlotElement& other);
 
     void updateDistributedNodesWithFallback();
 
+    void lazyReattachDistributedNodesIfNeeded();
+
     void attach(const AttachContext& = AttachContext()) final;
     void detach(const AttachContext& = AttachContext()) final;
 
     void attributeChanged(const QualifiedName&, const AtomicString& oldValue, const AtomicString& newValue, AttributeModificationReason = ModifiedDirectly) final;
 
     short tabIndex() const override;
     AtomicString name() const;
 
     // This method can be slow because this has to traverse the children of a shadow host.
     // This method should be used only when m_assignedNodes is dirty.
     // e.g. To detect a slotchange event in DOM mutations.
     bool hasAssignedNodesSlow() const;
     bool findHostChildWithSameSlotName() const;
 
     void enqueueSlotChangeEvent();
 
     void clearDistribution();
+    void saveAndClearDistribution();
 
     static AtomicString normalizeSlotName(const AtomicString&);
 
     DECLARE_VIRTUAL_TRACE();
 
 private:
     HTMLSlotElement(Document&);
 
     InsertionNotificationRequest insertedInto(ContainerNode*) final;
     void removedFrom(ContainerNode*) final;
     void willRecalcStyle(StyleRecalcChange) final;
 
     void dispatchSlotChangeEvent();
 
     HeapVector<Member<Node>> m_assignedNodes;
     HeapVector<Member<Node>> m_distributedNodes;
+    HeapVector<Member<Node>> m_oldDistributedNodes;
     HeapHashMap<Member<const Node>, size_t> m_distributedIndices;
     bool m_slotchangeEventEnqueued = false;
 };
 
 } // namespace blink
 
 #endif // HTMLSlotElement_h