Revert of Use registerWeakMembers to clean up IntersectionObserver.

third_party/WebKit/Source/core/dom/IntersectionObserver.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 IntersectionObserver_h
 #define IntersectionObserver_h
 
 #include "bindings/core/v8/ScriptWrappable.h"
 #include "core/dom/Element.h"
 #include "core/dom/IntersectionObservation.h"
 #include "core/dom/IntersectionObserverEntry.h"
 #include "platform/heap/Handle.h"
 #include "wtf/HashSet.h"
 #include "wtf/RefCounted.h"
 #include "wtf/Vector.h"
 
 namespace blink {
 
 class ExceptionState;
 class IntersectionObserverCallback;
 class IntersectionObserverInit;
 
 // TODO(oilpan): Switch to GarbageCollected<> after oilpan ships
 class IntersectionObserver final : public GarbageCollectedFinalized<IntersectionObserver>, public ScriptWrappable {
     DEFINE_WRAPPERTYPEINFO();
 
 public:
     static IntersectionObserver* create(const IntersectionObserverInit&, IntersectionObserverCallback&, ExceptionState&);
     static void resumeSuspendedObservers();
-    static void rootDisappearedCallback(Visitor*, void*);
 
     // API methods
     void observe(Element*, ExceptionState&);
     void unobserve(Element*, ExceptionState&);
     HeapVector<Member<IntersectionObserverEntry>> takeRecords();
 
     Node* root() const { return m_root.get(); }
     LayoutObject* rootLayoutObject() const;
     bool hasPercentMargin() const;
     const Length& topMargin() const { return m_topMargin; }
     const Length& rightMargin() const { return m_rightMargin; }
     const Length& bottomMargin() const { return m_bottomMargin; }
     const Length& leftMargin() const { return m_leftMargin; }
     bool isDescendantOfRoot(const Element*) const;
     void computeIntersectionObservations(double timestamp);
     void enqueueIntersectionObserverEntry(IntersectionObserverEntry&);
     void applyRootMargin(LayoutRect&) const;
     unsigned firstThresholdGreaterThan(float ratio) const;
     void deliver();
     void setActive(bool);
     void disconnect();
     void removeObservation(IntersectionObservation&);
     bool hasEntries() const { return m_entries.size(); }
 
     DECLARE_TRACE();
 
 private:
     explicit IntersectionObserver(IntersectionObserverCallback&, Node&, const Vector<Length>& rootMargin, const Vector<float>& thresholds);
 
+    void checkRootAndDetachIfNeeded();
+
     Member<IntersectionObserverCallback> m_callback;
     WeakPtrWillBeWeakMember<Node> m_root;
     HeapHashSet<WeakMember<IntersectionObservation>> m_observations;
     HeapVector<Member<IntersectionObserverEntry>> m_entries;
     Vector<float> m_thresholds;
     Length m_topMargin;
     Length m_rightMargin;
     Length m_bottomMargin;
     Length m_leftMargin;
 };
 
 } // namespace blink
 
 #endif // IntersectionObserver_h