Use registerWeakMembers to manage observer root.

third_party/WebKit/Source/core/dom/IntersectionObservation.cpp

 // 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.
 
 #include "core/dom/IntersectionObservation.h"
 
 #include "core/dom/ElementRareData.h"
 #include "core/dom/IntersectionObserver.h"
 #include "core/frame/FrameView.h"
 #include "core/layout/LayoutBox.h"
@@ skipping 143 matching lines @@
             pixelSnappedIntRect(geometry.rootRect),
             pixelSnappedIntRect(geometry.intersectionRect),
             targetElement);
         observer().enqueueIntersectionObserverEntry(*newEntry);
     }
     setLastThresholdIndex(newThresholdIndex);
 }
 
 void IntersectionObservation::disconnect()
 {
+    IntersectionObserver* observer = m_observer;
+    clearRootAndRemoveFromTarget();
+    observer->removeObservation(*this);
+}
+
+void IntersectionObservation::clearRootAndRemoveFromTarget()
+{
     if (m_target)
-        target()->ensureIntersectionObserverData().removeObservation(this->observer());
-    m_observer->removeObservation(*this);
+        target()->ensureIntersectionObserverData().removeObservation(observer());
     m_observer.clear();
 }
 
 DEFINE_TRACE(IntersectionObservation)
 {
     visitor->trace(m_observer);
     visitor->trace(m_target);
 }
 
 } // namespace blink