Replace RenderFullScreen with top layer

Source/core/css/resolver/StyleResolver.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 2004-2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2006, 2007 Nicholas Shanks (webkit@nickshanks.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007, 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (c) 2011, Code Aurora Forum. All rights reserved.
  * Copyright (C) Research In Motion Limited 2011. All rights reserved.
@@ skipping 862 matching lines @@
     RenderObject* parentRenderer = parent.renderer();
     if (!parentRenderer)
         return 0;
 
     if (pseudoId < FIRST_INTERNAL_PSEUDOID && !parentRenderer->style()->hasPseudoStyle(pseudoId))
         return 0;
 
     if (pseudoId == BACKDROP && !parent.isInTopLayer())
         return 0;
 
-    if (!parentRenderer->canHaveGeneratedChildren())
+    // It's safe to have a backdrop since its renderer is always a child of RenderView.
+    ASSERT(static_cast<RenderObject*>(parentRenderer->view())->canHaveGeneratedChildren());
+    if (pseudoId != BACKDROP && !parentRenderer->canHaveGeneratedChildren())
         return 0;
 
     RenderStyle* parentStyle = parentRenderer->style();
     StyleResolverState state(document(), &parent, parentStyle);
     if (!pseudoStyleForElementInternal(parent, pseudoId, parentStyle, state))
         return 0;
     RefPtr<RenderStyle> style = state.takeStyle();
     ASSERT(style);
 
     if (!pseudoElementRendererIsNeeded(style.get()))
@@ skipping 614 matching lines @@
 bool StyleResolver::mediaQueryAffectedByViewportChange() const
 {
     for (unsigned i = 0; i < m_viewportDependentMediaQueryResults.size(); ++i) {
         if (m_medium->eval(&m_viewportDependentMediaQueryResults[i]->m_expression) != m_viewportDependentMediaQueryResults[i]->m_result)
             return true;
     }
     return false;
 }
 
 } // namespace WebCore