Revert of Use registerWeakMembers to clean up IntersectionObserver.

third_party/WebKit/Source/core/dom/IntersectionObserver.h

Index: third_party/WebKit/Source/core/dom/IntersectionObserver.h
diff --git a/third_party/WebKit/Source/core/dom/IntersectionObserver.h b/third_party/WebKit/Source/core/dom/IntersectionObserver.h
index a918acb4cab2f8f6a182a4fbfbeecd9ebbc6672f..f793a6f958543add45b3d8b5810b6d6c2297357d 100644
--- a/third_party/WebKit/Source/core/dom/IntersectionObserver.h
+++ b/third_party/WebKit/Source/core/dom/IntersectionObserver.h
@@ -27,7 +27,6 @@
 public:
     static IntersectionObserver* create(const IntersectionObserverInit&, IntersectionObserverCallback&, ExceptionState&);
     static void resumeSuspendedObservers();
-    static void rootDisappearedCallback(Visitor*, void*);
 
     // API methods
     void observe(Element*, ExceptionState&);
@@ -57,6 +56,8 @@
 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;