Use registerWeakMembers to manage observer root.

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"
@@ skipping 37 matching lines @@
     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();
+#if ENABLE(OILPAN)
+    void clearWeakMembers(Visitor*);
+#endif
 
     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