[CSS Grid Layout] Upgrade justify-content parsing to CSS3 Box Alignment spec.

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 1355dad399ce294a5d34c4b0dc5f17899d8e7cfd..d30f5ac2c601417e19d6453f8cfe722f4041edb1 100644
--- a/Source/core/css/CSSValue.h
+++ b/Source/core/css/CSSValue.h
@@ -102,6 +102,7 @@ public:
     bool isFilterValue() const { return m_classType == CSSFilterClass; }
     bool isGridTemplateAreasValue() const { return m_classType == GridTemplateAreasClass; }
     bool isSVGDocumentValue() const { return m_classType == CSSSVGDocumentClass; }
+    bool isContentDistributionValue() const { return m_classType == CSSContentDistributionClass; }
     bool isUnicodeRangeValue() const { return m_classType == UnicodeRangeClass; }
     bool isGridLineNamesValue() const { return m_classType == GridLineNamesClass; }
 
@@ -161,6 +162,8 @@ protected:
         // SVG classes.
         CSSSVGDocumentClass,
 
+        CSSContentDistributionClass,
+
         // List class types must appear after ValueListClass.
         ValueListClass,
         ImageSetClass,