Implement proposed shadow tree cascade order.

Source/core/css/TreeBoundaryCrossingRules.h

-/*
- * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
- * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
- * Copyright (C) 2013 Google 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.
- *
- * This library is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
- * Library General Public License for more details.
- *
- * You should have received a copy of the GNU Library General Public License
- * along with this library; see the file COPYING.LIB.  If not, write to
- * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
- * Boston, MA 02110-1301, USA.
- *
- */
-
-#ifndef TreeBoundaryCrossingRules_h
-#define TreeBoundaryCrossingRules_h
-
-#include "core/dom/DocumentOrderedList.h"
-
-#include "wtf/OwnPtr.h"
-#include "wtf/RefPtr.h"
-#include "wtf/Vector.h"
-
-namespace blink {
-
-class ContainerNode;
-class Element;
-class ElementRuleCollector;
-
-class TreeBoundaryCrossingRules final {
-    DISALLOW_ALLOCATION();
-public:
-    void addScope(ContainerNode&);
-    void removeScope(const ContainerNode&);
-    void collectTreeBoundaryCrossingRules(Element*, ElementRuleCollector&, bool includeEmptyRules);
-
-    DECLARE_TRACE();
-
-private:
-    size_t size() const { return m_scopingNodes.size(); }
-
-    DocumentOrderedList m_scopingNodes;
-};
-
-} // namespace blink
-
-#endif // TreeBoundaryCrossingRules_h