ElementVisibilityObserver: get rid of reference cycle.

third_party/WebKit/Source/core/dom/ElementVisibilityObserver.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/ElementVisibilityObserver.h"
 
 #include "core/dom/Element.h"
 #include "core/dom/IntersectionObserverEntry.h"
 #include "wtf/Functional.h"
 
 namespace blink {
 
 ElementVisibilityObserver::ElementVisibilityObserver(Element* element, std::unique_ptr<VisibilityCallback> callback)
     : m_element(element)
     , m_callback(std::move(callback))
 {
 }
 
 ElementVisibilityObserver::~ElementVisibilityObserver() = default;
 
 void ElementVisibilityObserver::start()
 {
     DCHECK(!m_intersectionObserver);
     m_intersectionObserver = IntersectionObserver::create(
         Vector<Length>(), Vector<float>({std::numeric_limits<float>::min()}), &m_element->document(),
         WTF::bind(&ElementVisibilityObserver::onVisibilityChanged, wrapWeakPersistent(this)));
     DCHECK(m_intersectionObserver);
-    m_intersectionObserver->observe(m_element);
+    m_intersectionObserver->observe(m_element.release());
 }
 
 void ElementVisibilityObserver::stop()
 {
     DCHECK(m_intersectionObserver);
 
-    m_intersectionObserver->unobserve(m_element);
+    m_intersectionObserver->disconnect();
     m_intersectionObserver = nullptr;
 }
 
 DEFINE_TRACE(ElementVisibilityObserver)
 {
     visitor->trace(m_element);
     visitor->trace(m_intersectionObserver);
 }
 
 void ElementVisibilityObserver::onVisibilityChanged(const HeapVector<Member<IntersectionObserverEntry>>& entries)
 {
     bool isVisible = entries.last()->intersectionRatio() > 0.f;
     (*m_callback.get())(isVisible);
 }
 
 } // namespace blink