Add backup element queue to CustomElementReactionStack

third_party/WebKit/Source/core/dom/custom/CustomElementReactionStack.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 CustomElementReactionStack_h
 #define CustomElementReactionStack_h
 
 #include "core/CoreExport.h"
 #include "platform/heap/Handle.h"
 #include "wtf/Noncopyable.h"
 
 namespace blink {
 
 class CustomElementReaction;
 class CustomElementReactionQueue;
 class Element;
 
 // https://html.spec.whatwg.org/multipage/scripting.html#custom-element-reactions
 class CORE_EXPORT CustomElementReactionStack final
     : public GarbageCollected<CustomElementReactionStack> {
     WTF_MAKE_NONCOPYABLE(CustomElementReactionStack);
 public:
     CustomElementReactionStack();
 
     DECLARE_TRACE();
 
     void push();
     void popInvokingReactions();
-    void enqueue(Element*, CustomElementReaction*);
+    void enqueueToCurrentQueue(Element*, CustomElementReaction*);
+    void enqueueToBackupQueue(Element*, CustomElementReaction*);
 
 private:
     using ElementReactionQueueMap =
         HeapHashMap<Member<Element>, Member<CustomElementReactionQueue>>;
     ElementReactionQueueMap m_map;
 
     using ElementQueue = HeapVector<Member<Element>, 1>;
     HeapVector<Member<ElementQueue>> m_stack;
+    Member<ElementQueue> m_backupQueue;
+
+    void invokeBackupQueue();
+    void invokeReactions(ElementQueue&);
+    void enqueue(Member<ElementQueue>&, Element*, CustomElementReaction*);
 };
 
 } // namespace blink
 
 #endif // CustomElementReactionStack_h