[CSS Grid Layout] Implement 'justify-items' parsing

Source/core/frame/UseCounter.cpp

Index: Source/core/frame/UseCounter.cpp
diff --git a/Source/core/frame/UseCounter.cpp b/Source/core/frame/UseCounter.cpp
index a25946e078acdad385773c3e16865a4940cd90f3..fe85008d6bf1711895a17e654c181166e9552758 100644
--- a/Source/core/frame/UseCounter.cpp
+++ b/Source/core/frame/UseCounter.cpp
@@ -509,6 +509,7 @@ int UseCounter::mapCSSPropertyIdToCSSSampleIdForHistogram(int id)
     case CSSPropertyBackfaceVisibility: return 451;
     case CSSPropertyGridTemplate: return 452;
     case CSSPropertyGrid: return 453;
+    case CSSPropertyJustifyItems: return 454;
 
     // 1. Add new features above this line (don't change the assigned numbers of the existing
     // items).
@@ -531,7 +532,7 @@ int UseCounter::mapCSSPropertyIdToCSSSampleIdForHistogram(int id)
     return 0;
 }
 
-static int maximumCSSSampleId() { return 453; }
+static int maximumCSSSampleId() { return 454; }
 
 void UseCounter::muteForInspector()
 {