Use the tree of trees for the lang attributes in Shadow DOM

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 2559 matching lines @@
                 if (const Attribute* attribute = attributes.find(XMLNames::langAttr))
                     value = attribute->value();
                 else if (const Attribute* attribute = attributes.find(HTMLNames::langAttr))
                     value = attribute->value();
             }
         } else if (n->isDocumentNode()) {
             // checking the MIME content-language
             value = toDocument(n)->contentLanguage();
         }
 
-        n = n->parentNode();
+        n = n->parentOrShadowHostNode();
     } while (n && value.isNull());
 
     return value;
 }
 
 Locale& Element::locale() const
 {
     return document().getCachedLocale(computeInheritedLanguage());
 }
 
@@ skipping 795 matching lines @@
 {
 #if ENABLE(OILPAN)
     if (hasRareData())
         visitor->trace(elementRareData());
     visitor->trace(m_elementData);
 #endif
     ContainerNode::trace(visitor);
 }
 
 } // namespace blink