Removed unused scrollbar pseudo classes.

Source/core/css/CSSSelector.h

 /*
  * Copyright (C) 1999-2003 Lars Knoll (knoll@kde.org)
  *               1999 Waldo Bastian (bastian@kde.org)
  * Copyright (C) 2004, 2006, 2007, 2008, 2009, 2010, 2013 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 162 matching lines @@
             PseudoTarget,
             PseudoBefore,
             PseudoAfter,
             PseudoBackdrop,
             PseudoLang,
             PseudoNot,
             PseudoResizer,
             PseudoRoot,
             PseudoScope,
             PseudoScrollbar,
-            PseudoScrollbarBack,
             PseudoScrollbarButton,
             PseudoScrollbarCorner,
-            PseudoScrollbarForward,
             PseudoScrollbarThumb,
             PseudoScrollbarTrack,
             PseudoScrollbarTrackPiece,
             PseudoWindowInactive,
             PseudoCornerPresent,
             PseudoDecrement,
             PseudoIncrement,
             PseudoHorizontal,
             PseudoVertical,
             PseudoStart,
@@ skipping 341 matching lines @@
     if (m_hasRareData)
         return m_data.m_rareData->m_value;
     // AtomicString is really just a StringImpl* so the cast below is safe.
     // FIXME: Perhaps call sites could be changed to accept StringImpl?
     return *reinterpret_cast<const AtomicString*>(&m_data.m_value);
 }
 
 } // namespace blink
 
 #endif // CSSSelector_h