Implement unset value handling

Source/core/css/CSSValue.h

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 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,
@@ skipping 49 matching lines @@
     bool isFontFeatureValue() const { return m_classType == FontFeatureClass; }
     bool isFontValue() const { return m_classType == FontClass; }
     bool isFontFaceSrcValue() const { return m_classType == FontFaceSrcClass; }
     bool isFunctionValue() const { return m_classType == FunctionClass; }
     bool isImageGeneratorValue() const { return m_classType >= CanvasClass && m_classType <= RadialGradientClass; }
     bool isGradientValue() const { return m_classType >= LinearGradientClass && m_classType <= RadialGradientClass; }
     bool isImageSetValue() const { return m_classType == ImageSetClass; }
     bool isImageValue() const { return m_classType == ImageClass; }
     bool isImplicitInitialValue() const;
     bool isInheritedValue() const { return m_classType == InheritedClass; }
+    bool isUnsetValue() const { return m_classType == UnsetClass; }
     bool isInitialValue() const { return m_classType == InitialClass; }
     bool isLinearGradientValue() const { return m_classType == LinearGradientClass; }
     bool isRadialGradientValue() const { return m_classType == RadialGradientClass; }
     bool isReflectValue() const { return m_classType == ReflectClass; }
     bool isShadowValue() const { return m_classType == ShadowClass; }
     bool isCubicBezierTimingFunctionValue() const { return m_classType == CubicBezierTimingFunctionClass; }
     bool isStepsTimingFunctionValue() const { return m_classType == StepsTimingFunctionClass; }
     bool isTransformValue() const { return m_classType == CSSTransformClass; }
     bool isLineBoxContainValue() const { return m_classType == LineBoxContainClass; }
     bool isCalcValue() const {return m_classType == CalculationClass; }
@@ skipping 34 matching lines @@
 
         // Other class types.
         BorderImageSliceClass,
         FontFeatureClass,
         FontClass,
         FontFaceSrcClass,
         FunctionClass,
 
         InheritedClass,
         InitialClass,
+        UnsetClass,
 
         ReflectClass,
         ShadowClass,
         UnicodeRangeClass,
         LineBoxContainClass,
         CalculationClass,
         GridTemplateAreasClass,
 
         // SVG classes.
         CSSSVGDocumentClass,
@@ skipping 86 matching lines @@
 {
     return first ? second && first->equals(*second) : !second;
 }
 
 #define DEFINE_CSS_VALUE_TYPE_CASTS(thisType, predicate) \
     DEFINE_TYPE_CASTS(thisType, CSSValue, value, value->predicate, value.predicate)
 
 } // namespace blink
 
 #endif // CSSValue_h