Be more strict about multiple documentElements

Source/core/dom/Document.h

 /*
  * 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, 2010, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
@@ skipping 644 matching lines @@
 
     void attachRange(Range*);
     void detachRange(Range*);
 
     void updateRangesAfterChildrenChanged(ContainerNode*);
     void updateRangesAfterNodeMovedToAnotherDocument(const Node&);
     // nodeChildrenWillBeRemoved is used when removing all node children at once.
     void nodeChildrenWillBeRemoved(ContainerNode&);
     // nodeWillBeRemoved is only safe when removing one node at a time.
     void nodeWillBeRemoved(Node&);
-    bool canReplaceChild(const Node& newChild, const Node& oldChild) const;
+    bool canAcceptChild(const Node& newChild, const Node* oldChild, ExceptionState&) const;
 
     void didInsertText(Node*, unsigned offset, unsigned length);
     void didRemoveText(Node*, unsigned offset, unsigned length);
     void didMergeTextNodes(Text& oldNode, unsigned offset);
     void didSplitTextNode(Text& oldNode);
 
     void clearDOMWindow() { m_domWindow = nullptr; }
     LocalDOMWindow* domWindow() const { return m_domWindow; }
 
     // Helper functions for forwarding LocalDOMWindow event related tasks to the LocalDOMWindow if it exists.
@@ skipping 746 matching lines @@
 DEFINE_TYPE_CASTS(TreeScope, Document, document, true, true);
 
 } // namespace blink
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showLiveDocumentInstances();
 #endif
 
 #endif // Document_h