Custom Elements in template should not be upgraded

Source/core/dom/Document.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, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2008, 2009, 2011, 2012 Google Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) Research In Motion Limited 2010-2011. All rights reserved.
@@ skipping 975 matching lines @@
             return nullptr;
         }
         RefPtrWillBeRawPtr<Element> newElement = createElement(oldElement->tagQName(), false);
 
         newElement->cloneDataFromElement(*oldElement);
 
         if (deep) {
             if (!importContainerNodeChildren(oldElement, newElement, exceptionState))
                 return nullptr;
             if (isHTMLTemplateElement(*oldElement)
-                && !importContainerNodeChildren(toHTMLTemplateElement(oldElement)->content(), toHTMLTemplateElement(newElement)->content(), exceptionState))
+                && !ensureTemplateDocument().importContainerNodeChildren(
+                    toHTMLTemplateElement(oldElement)->content(),
+                    toHTMLTemplateElement(newElement)->content(), exceptionState))
                 return nullptr;
         }
 
         return newElement.release();
     }
     case ATTRIBUTE_NODE:
         return Attr::create(*this, QualifiedName(nullAtom, AtomicString(toAttr(importedNode)->name()), nullAtom), toAttr(importedNode)->value());
     case DOCUMENT_FRAGMENT_NODE: {
         if (importedNode->isShadowRoot()) {
             // ShadowRoot nodes should not be explicitly importable.
@@ skipping 4823 matching lines @@
 #ifndef NDEBUG
 using namespace blink;
 void showLiveDocumentInstances()
 {
     WeakDocumentSet& set = liveDocumentSet();
     fprintf(stderr, "There are %u documents currently alive:\n", set.size());
     for (Document* document : set)
         fprintf(stderr, "- Document %p URL: %s\n", document, document->url().string().utf8().data());
 }
 #endif