Replace RenderFullScreen with top layer

Source/core/dom/Element.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Peter Kelly (pmk@post.com)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012, 2013 Apple Inc. All rights reserved.
  *           (C) 2007 Eric Seidel (eric@webkit.org)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 2775 matching lines @@
     } else if (change >= Inherit || needsStyleRecalc())
         createPseudoElementIfNeeded(pseudoId);
 }
 
 bool Element::needsPseudoElement(PseudoId pseudoId, const RenderStyle& style) const
 {
     if (pseudoId == BACKDROP && !isInTopLayer())
         return false;
     if (!renderer() || !pseudoElementRendererIsNeeded(&style))
         return false;
-    if (!renderer()->canHaveGeneratedChildren())
+    /* It's safe to have a backdrop since its renderer is always a child of RenderView. */
+    if (pseudoId != BACKDROP && !renderer()->canHaveGeneratedChildren())
         return false;
     return true;
 }
 
 void Element::createPseudoElementIfNeeded(PseudoId pseudoId)
 {
     if (isPseudoElement())
         return;
 
     RefPtr<PseudoElement> element = document().ensureStyleResolver().createPseudoElementIfNeeded(*this, pseudoId);
@@ skipping 831 matching lines @@
     // Before doing so, we need to resolve issues in HTMLSelectElement::recalcListItems
     // and RenderMenuList::setText. See also https://bugs.webkit.org/show_bug.cgi?id=88405
     if (hasTagName(optionTag) || hasTagName(optgroupTag))
         return false;
     if (FullscreenElementStack::isActiveFullScreenElement(this))
         return false;
     return true;
 }
 
 } // namespace WebCore