ElementVisibilityObserver: get rid of reference cycle.

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

Index: third_party/WebKit/Source/core/dom/ElementVisibilityObserver.cpp
diff --git a/third_party/WebKit/Source/core/dom/ElementVisibilityObserver.cpp b/third_party/WebKit/Source/core/dom/ElementVisibilityObserver.cpp
index d8510e5b2f3c89ce163f74f4c6119939b50853c5..05f571387aa193c7b7269add45af7a5d4eb69c03 100644
--- a/third_party/WebKit/Source/core/dom/ElementVisibilityObserver.cpp
+++ b/third_party/WebKit/Source/core/dom/ElementVisibilityObserver.cpp
@@ -25,14 +25,14 @@ void ElementVisibilityObserver::start()
         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;
 }