Fixing crash in AutoplayUmaHelper when registering unload event listener

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 55 matching lines @@
     DEFINE_STATIC_LOCAL(EnumerationHistogram, autoplayUnmuteHistogram, ("Media.Video.Autoplay.Muted.UnmuteAction", static_cast<int>(AutoplayUnmuteActionStatus::NumberOfStatus)));
 
     autoplayUnmuteHistogram.count(static_cast<int>(status));
 }
 
 void AutoplayUmaHelper::didMoveToNewDocument(Document& oldDocument)
 {
     if (!m_videoMutedPlayMethodVisibilityObserver)
         return;
 
-    oldDocument.domWindow()->removeEventListener(EventTypeNames::unload, this, false);
-    m_element->document().domWindow()->addEventListener(EventTypeNames::unload, this, false);
+    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)
         return;
 
     recordVideoAutoplayMutedPlayMethodBecomesVisibleUma(true);
     m_videoMutedPlayMethodVisibilityObserver->stop();
     m_videoMutedPlayMethodVisibilityObserver = nullptr;
-    m_element->document().domWindow()->removeEventListener(EventTypeNames::unload, this, false);
+    if (m_element && m_element->document().domWindow())
+        m_element->document().domWindow()->removeEventListener(EventTypeNames::unload, this, false);
 }
 
 void AutoplayUmaHelper::handleEvent(ExecutionContext* executionContext, Event* event)
 {
     if (event->type() == EventTypeNames::playing)
         handlePlayingEvent();
     else if (event->type() == EventTypeNames::unload)
         handleUnloadEvent();
     else
         NOTREACHED();
@@ skipping 22 matching lines @@
 }
 
 DEFINE_TRACE(AutoplayUmaHelper)
 {
     EventListener::trace(visitor);
     visitor->trace(m_element);
     visitor->trace(m_videoMutedPlayMethodVisibilityObserver);
 }
 
 } // namespace blink