[CSS Grid Layout] Update named grid lines syntax to the last version of the specs

Source/core/css/CSSValue.h

Index: Source/core/css/CSSValue.h
diff --git a/Source/core/css/CSSValue.h b/Source/core/css/CSSValue.h
index 76c04cb87585d064aaf2f9f06793a25dd5f8f67c..6e1b283ad6e2c58dccd006eb636b3082f682df98 100644
--- a/Source/core/css/CSSValue.h
+++ b/Source/core/css/CSSValue.h
@@ -105,6 +105,7 @@ public:
     bool isSVGPaint() const { return m_classType == SVGPaintClass; }
     bool isSVGDocumentValue() const { return m_classType == CSSSVGDocumentClass; }
     bool isUnicodeRangeValue() const { return m_classType == UnicodeRangeClass; }
+    bool isGridLineNamesValue() const { return m_classType == GridLineNamesClass; }
 
     bool isCSSOMSafe() const { return m_isCSSOMSafe; }
     bool isSubtypeExposedToCSSOM() const
@@ -172,6 +173,7 @@ protected:
         CSSArrayFunctionValueClass,
         CSSMixFunctionValueClass,
         CSSTransformClass,
+        GridLineNamesClass,
         // Do not append non-list class types here.
     };