Clarify FullscreenElementStack::addDocumentToFullScreenChangeEventQueue

Source/core/dom/FullscreenElementStack.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
@@ skipping 548 matching lines @@
     m_fullScreenElementStack.removeLast();
 }
 
 void FullscreenElementStack::pushFullscreenElementStack(Element& element)
 {
     m_fullScreenElementStack.append(&element);
 }
 
 void FullscreenElementStack::addDocumentToFullScreenChangeEventQueue(Document& doc)
 {
-    Node* target = 0;
-    if (FullscreenElementStack* fullscreen = fromIfExists(doc)) {
-        target = fullscreen->webkitFullscreenElement();
-        if (!target)
-            target = fullscreen->webkitCurrentFullScreenElement();
-    }
+    ASSERT(doc.hasFullscreenElementStack());
+    FullscreenElementStack& fullscreen = from(doc);
 
+    Node* target = fullscreen.webkitFullscreenElement();
+    if (!target)
+        target = fullscreen.webkitCurrentFullScreenElement();
     if (!target)
         target = &doc;
     m_fullScreenChangeEventTargetQueue.append(target);
 }
 
 void FullscreenElementStack::trace(Visitor* visitor)
 {
     visitor->trace(m_fullScreenElement);
     visitor->trace(m_fullScreenElementStack);
     visitor->trace(m_fullScreenChangeEventTargetQueue);
     visitor->trace(m_fullScreenErrorEventTargetQueue);
     DocumentSupplement::trace(visitor);
 }
 
 } // namespace WebCore