Don't allow style sharing between top layer and non-top layer elements

Source/core/css/resolver/SharedStyleFinder.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 191 matching lines @@
     if (!sharingCandidateHasIdenticalStyleAffectingAttributes(candidate))
         return false;
     if (candidate.additionalPresentationAttributeStyle() != element().additionalPresentationAttributeStyle())
         return false;
     if (candidate.hasID() && m_features.hasSelectorForId(candidate.idForStyleResolution()))
         return false;
     if (candidate.hasScopedHTMLStyleChild())
         return false;
     if (candidate.shadow() && candidate.shadow()->containsActiveStyles() && !sharingCandidateShadowHasSharedStyleSheetContents(candidate))
         return false;
+    if (candidate.isInTopLayer() != element().isInTopLayer())
+        return false;
 
     bool isControl = candidate.isFormControlElement();
 
     if (isControl != element().isFormControlElement())
         return false;
 
     if (isControl && !canShareStyleWithControl(candidate))
         return false;
 
     // FIXME: This line is surprisingly hot, we may wish to inline hasDirectionAuto into StyleResolver.
@@ skipping 92 matching lines @@
     // Tracking child index requires unique style for each node. This may get set by the sibling rule match above.
     if (!element().parentOrShadowHostElement()->childrenSupportStyleSharing()) {
         INCREMENT_STYLE_STATS_COUNTER(m_styleResolver, sharedStyleRejectedByParent);
         return 0;
     }
 
     return shareElement->renderStyle();
 }
 
 }