Implement 'scroll-behavior' parsing

Source/core/rendering/style/StyleRareNonInheritedData.h

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2003, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *
  * 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
@@ skipping 179 matching lines @@
 
     unsigned m_touchAction : TouchActionBits; // TouchAction
 
     unsigned m_objectFit : 3; // ObjectFit
 
     unsigned m_isolation : 1; // Isolation
 
     unsigned m_justifySelf : 4; // ItemPosition
     unsigned m_justifySelfOverflowAlignment : 2; // OverflowAlignment
 
+    unsigned m_scrollBehavior: 2; // ScrollBehavior

[Julien - ping for review, 2014/01/22 16:24:35]

It's bad that we are using an extra bit for no good reason: the accepted values
are "instant" or "smooth" which is really a binary choice. I don't think we
should modify the code though but maybe worth mentioning it in a comment?

[ajuma, 2014/01/22 19:50:20]

Added a comment.

+
 private:
     StyleRareNonInheritedData();
     StyleRareNonInheritedData(const StyleRareNonInheritedData&);
 };
 
 } // namespace WebCore
 
 #endif // StyleRareNonInheritedData_h