Fix a crash in AutoplayUmaHelper when releasing visibility observer

third_party/WebKit/Source/core/html/AutoplayUmaHelper.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/html/AutoplayUmaHelper.h"
 
 #include "core/dom/Document.h"
 #include "core/dom/ElementVisibilityObserver.h"
 #include "core/events/Event.h"
 #include "core/frame/LocalDOMWindow.h"
@@ skipping 63 matching lines @@
         return;
 
     if (oldDocument.domWindow())
         oldDocument.domWindow()->removeEventListener(EventTypeNames::unload, this, false);
     if (m_element && m_element->document().domWindow())
         m_element->document().domWindow()->addEventListener(EventTypeNames::unload, this, false);
 }
 
 void AutoplayUmaHelper::onVisibilityChangedForVideoMutedPlayMethod(bool isVisible)
 {
-    if (!isVisible)
+    if (!isVisible || !m_videoMutedPlayMethodVisibilityObserver)
         return;
 
     recordVideoAutoplayMutedPlayMethodBecomesVisibleUma(true);
     m_videoMutedPlayMethodVisibilityObserver->stop();
     m_videoMutedPlayMethodVisibilityObserver = nullptr;
     if (m_element && m_element->document().domWindow())
         m_element->document().domWindow()->removeEventListener(EventTypeNames::unload, this, false);
 }
 
 void AutoplayUmaHelper::handleEvent(ExecutionContext* executionContext, Event* event)
@@ skipping 13 matching lines @@
         m_videoMutedPlayMethodVisibilityObserver->stop();
         m_videoMutedPlayMethodVisibilityObserver = nullptr;
         m_element->document().domWindow()->removeEventListener(EventTypeNames::unload, this, false);
     }
 }
 
 void AutoplayUmaHelper::handlePlayingEvent()
 {
     if (m_source == AutoplaySource::Method && m_element->isHTMLVideoElement() && m_element->muted()) {
         if (!m_videoMutedPlayMethodVisibilityObserver) {
-            m_videoMutedPlayMethodVisibilityObserver = new ElementVisibilityObserver(m_element, WTF::bind(&AutoplayUmaHelper::onVisibilityChangedForVideoMutedPlayMethod, wrapPersistent(this)));
+            m_videoMutedPlayMethodVisibilityObserver = new ElementVisibilityObserver(m_element, WTF::bind(&AutoplayUmaHelper::onVisibilityChangedForVideoMutedPlayMethod, wrapWeakPersistent(this)));
             m_videoMutedPlayMethodVisibilityObserver->start();
             m_element->document().domWindow()->addEventListener(EventTypeNames::unload, this, false);
         }
     }
     m_element->removeEventListener(EventTypeNames::playing, this, false);
 }
 
 DEFINE_TRACE(AutoplayUmaHelper)
 {
     EventListener::trace(visitor);
     visitor->trace(m_element);
     visitor->trace(m_videoMutedPlayMethodVisibilityObserver);
 }
 
 } // namespace blink