Reduce forward declarations in core/dom

Source/core/dom/DocumentFragment.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2009 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 11 matching lines @@
  */
 
 #ifndef DocumentFragment_h
 #define DocumentFragment_h
 
 #include "core/dom/ContainerNode.h"
 #include "core/dom/ParserContentPolicy.h"
 
 namespace WebCore {
 
-class ExecutionContext;
-
 class DocumentFragment : public ContainerNode {
 public:
     static PassRefPtrWillBeRawPtr<DocumentFragment> create(Document&);
 
     void parseHTML(const String&, Element* contextElement, ParserContentPolicy = AllowScriptingContent);
     bool parseXML(const String&, Element* contextElement, ParserContentPolicy = AllowScriptingContent);
 
     virtual bool canContainRangeEndPoint() const OVERRIDE FINAL { return true; }
     virtual bool isTemplateContent() const { return false; }
 
 protected:
     DocumentFragment(Document*, ConstructionType = CreateContainer);
     virtual String nodeName() const OVERRIDE FINAL;
 
 private:
     virtual NodeType nodeType() const OVERRIDE FINAL;
     virtual PassRefPtrWillBeRawPtr<Node> cloneNode(bool deep = true) OVERRIDE;
     virtual bool childTypeAllowed(NodeType) const OVERRIDE;
 };
 
 DEFINE_NODE_TYPE_CASTS(DocumentFragment, isDocumentFragment());
 
 } // namespace WebCore
 
 #endif