Make custom elements work in HTML imports

third_party/WebKit/Source/core/dom/custom/CustomElementUpgradeSorter.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CustomElementUpgradeSorter_h
 #define CustomElementUpgradeSorter_h
 
 #include "core/CoreExport.h"
 #include "platform/heap/Handle.h"
 
@@ skipping 16 matching lines @@
     // Adds shadow-including descendents of parent to result in
     // shadow-including tree order. This operation is destroys the
     // state of this sorter; after calling sorted, you must not call
     // add or sorted again with this object.
     void sorted(HeapVector<Member<Element>>* result, Node* parent);
 
 private:
     using ChildSet = HeapHashSet<Member<Node>>;
     using ParentChildMap = HeapHashMap<Member<Node>, ChildSet>;
 
+    enum AddResult {
+        kParentAlreadyExistsInMap,
+        kParentAddedToMap
+    };
+
+    AddResult addToParentChildMap(Node* parent, Node* child);
     void visit(
         HeapVector<Member<Element>>* result,
         ChildSet&,
         const ChildSet::iterator&);
 
     Member<HeapHashSet<Member<Element>>> m_elements;
 
     // This is the subset of the tree, from root node (usually
     // document) through elements and shadow roots, to candidates.
     Member<ParentChildMap> m_parentChildMap;
 };
 
 } // namespace blink
 
 #endif // CustomElementUpgradeSorter_h