Upgrade stepUp()/stepDown() implementation to match spec.

Source/core/html/forms/StepRange.h

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010 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.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 53 matching lines @@
 
         Decimal defaultValue() const
         {
             return defaultStep * stepScaleFactor;
         }
     };
 
     StepRange();
     StepRange(const StepRange&);
     StepRange(const Decimal& stepBase, const Decimal& minimum, const Decimal& maximum, const Decimal& step, const StepDescription&);
-    Decimal acceptableError() const;
     Decimal alignValueForStep(const Decimal& currentValue, const Decimal& newValue) const;
     Decimal clampValue(const Decimal& value) const;
     bool hasStep() const { return m_hasStep; }
     Decimal maximum() const { return m_maximum; }
     Decimal minimum() const { return m_minimum; }
     static Decimal parseStep(AnyStepHandling, const StepDescription&, const String&);
     Decimal step() const { return m_step; }
     Decimal stepBase() const { return m_stepBase; }
     bool stepMismatch(const Decimal&) const;
 
@@ skipping 13 matching lines @@
     }
 
     // Map from 0-1 range to value
     Decimal valueFromProportion(const Decimal& proportion) const
     {
         return m_minimum + proportion * (m_maximum - m_minimum);
     }
 
 private:
     StepRange& operator =(const StepRange&);
+    Decimal acceptableError() const;
     Decimal roundByStep(const Decimal& value, const Decimal& base) const;
 
     const Decimal m_maximum; // maximum must be >= minimum.
     const Decimal m_minimum;
     const Decimal m_step;
     const Decimal m_stepBase;
     const StepDescription m_stepDescription;
     const bool m_hasStep;
 };
 
 }
 
 #endif // StepRange_h