Reland of Fix FlatTreeTraversal for a slot in a document tree

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 75 matching lines @@
   // 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();
 
+  bool supportsDistribution() const { return isInShadowTree(); }
+  void updateDistributedNodesManually();
+
   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