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

Source/core/html/forms/StepRange.cpp

 /*
  * 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 143 matching lines @@
     // Decimal's fractional part size is DBL_MAN_DIG-bit. If the current value
     // is greater than step*2^DBL_MANT_DIG, the following computation for
     // remainder makes no sense.
     DEFINE_STATIC_LOCAL(const Decimal, twoPowerOfDoubleMantissaBits, (Decimal::Positive, 0, UINT64_C(1) << DBL_MANT_DIG));
     if (value / twoPowerOfDoubleMantissaBits > m_step)
         return false;
     // The computation follows HTML5 4.10.7.2.10 `The step attribute' :
     // ... that number subtracted from the step base is not an integral multiple
     // of the allowed value step, the element is suffering from a step mismatch.
     const Decimal remainder = (value - m_step * (value / m_step).round()).abs();
-    // Accepts erros in lower fractional part which IEEE 754 single-precision
+    // Accepts errors in lower fractional part which IEEE 754 single-precision
     // can't represent.
     const Decimal computedAcceptableError = acceptableError();
     return computedAcceptableError < remainder && remainder < (m_step - computedAcceptableError);
 }
 
 } // namespace WebCore