Have ProcessingInstruction's XSLT event listener keep a weak backreference

Source/core/dom/ProcessingInstruction.h

 /*
  * Copyright (C) 2000 Peter Kelly (pmk@post.com)
  * Copyright (C) 2006 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 37 matching lines @@
     StyleSheet* sheet() const { return m_sheet.get(); }
     void setCSSStyleSheet(PassRefPtrWillBeRawPtr<CSSStyleSheet>);
 
     bool isCSS() const { return m_isCSS; }
     bool isXSL() const { return m_isXSL; }
 
     void didAttributeChanged();
     bool isLoading() const;
 
     // For XSLT
-    void setEventListenerForXSLT(PassRefPtr<EventListener> listener) { m_listenerForXSLT = listener; }
-    EventListener* eventListenerForXSLT() { return m_listenerForXSLT.get(); }
-    void clearEventListenerForXSLT() { m_listenerForXSLT.clear(); }
+    class DetachableEventListener {
+    public:
+        virtual ~DetachableEventListener() { }
+
+        void ref() { refDetachableEventListener(); }
+        void deref() { derefDetachableEventListener(); }
+
+        virtual EventListener* toEventListener() = 0;
+
+        // Detach event listener from its processing instruction.
+        virtual void detach() = 0;
+
+    private:
+        virtual void refDetachableEventListener() = 0;
+        virtual void derefDetachableEventListener() = 0;
+    };
+
+    void setEventListenerForXSLT(PassRefPtr<DetachableEventListener> listener) { m_listenerForXSLT = listener; }
+    EventListener* eventListenerForXSLT();
+    void clearEventListenerForXSLT();
 
 private:
     ProcessingInstruction(Document&, const String& target, const String& data);
 
     virtual String nodeName() const override;
     virtual NodeType nodeType() const override;
     virtual PassRefPtrWillBeRawPtr<Node> cloneNode(bool deep = true) override;
 
     virtual InsertionNotificationRequest insertedInto(ContainerNode*) override;
     virtual void removedFrom(ContainerNode*) override;
@@ skipping 13 matching lines @@
     String m_localHref;
     String m_title;
     String m_media;
     RefPtrWillBeMember<StyleSheet> m_sheet;
     bool m_loading;
     bool m_alternate;
     bool m_createdByParser;
     bool m_isCSS;
     bool m_isXSL;
 
-    RefPtr<EventListener> m_listenerForXSLT;
+    RefPtr<DetachableEventListener> m_listenerForXSLT;
 };
 
 DEFINE_NODE_TYPE_CASTS(ProcessingInstruction, nodeType() == Node::PROCESSING_INSTRUCTION_NODE);
 
 inline bool isXSLStyleSheet(const Node& node)
 {
     return node.nodeType() == Node::PROCESSING_INSTRUCTION_NODE && toProcessingInstruction(node).isXSL();
 }
 
 } // namespace blink
 
 #endif // ProcessingInstruction_h