Make TreeScopeEventContext have a RefPtr to TreeScope.rootNode to guard TreeScope.

Source/core/events/TreeScopeEventContext.h

 /*
  * Copyright (C) 2014 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 33 matching lines @@
 class TouchEventContext;
 class TreeScope;
 
 class TreeScopeEventContext final : public RefCountedWillBeGarbageCollected<TreeScopeEventContext> {
     DECLARE_EMPTY_DESTRUCTOR_WILL_BE_REMOVED(TreeScopeEventContext);
 public:
     static PassRefPtrWillBeRawPtr<TreeScopeEventContext> create(TreeScope&);
     void trace(Visitor*);
 
     TreeScope& treeScope() const { return *m_treeScope; }
+    Node& rootNode() const { return *m_rootNode; }
 
     EventTarget* target() const { return m_target.get(); }
     void setTarget(PassRefPtrWillBeRawPtr<EventTarget>);
 
     EventTarget* relatedTarget() const { return m_relatedTarget.get(); }
     void setRelatedTarget(PassRefPtrWillBeRawPtr<EventTarget>);
 
     TouchEventContext* touchEventContext() const { return m_touchEventContext.get(); }
     TouchEventContext* ensureTouchEventContext();
 
     PassRefPtrWillBeRawPtr<StaticNodeList> ensureEventPath(EventPath&);
 
     bool isInclusiveAncestorOf(const TreeScopeEventContext&);
     void addChild(TreeScopeEventContext& child) { m_children.append(&child); }
 
     // For ancestor-descendant relationship check in Q(1).
     // Preprocessing takes O(N).
     int calculatePrePostOrderNumber(int orderNumber);
 
 private:
     TreeScopeEventContext(TreeScope&);
 
 #if ENABLE(ASSERT)
     bool isUnreachableNode(EventTarget&);
 #endif
 
     RawPtrWillBeMember<TreeScope> m_treeScope;
+    RefPtrWillBeMember<Node> m_rootNode; // Prevents TreeScope from being freed. TreeScope itself isn't RefCounted.
     RefPtrWillBeMember<EventTarget> m_target;
     RefPtrWillBeMember<EventTarget> m_relatedTarget;
     RefPtrWillBeMember<StaticNodeList> m_eventPath;
     RefPtrWillBeMember<TouchEventContext> m_touchEventContext;
 
     WillBeHeapVector<RawPtrWillBeMember<TreeScopeEventContext>> m_children;
     int m_preOrder;
     int m_postOrder;
 };
 
@@ skipping 21 matching lines @@
 
 inline bool TreeScopeEventContext::isInclusiveAncestorOf(const TreeScopeEventContext& other)
 {
     ASSERT(m_preOrder != -1 && m_postOrder != -1 && other.m_preOrder != -1 && other.m_postOrder != -1);
     return m_preOrder <= other.m_preOrder && other.m_postOrder <= m_postOrder;
 }
 
 }
 
 #endif // TreeScopeEventContext_h