[CSS Grid Layout] Named grid line span not allowed for automatic positions

Source/core/rendering/style/GridCoordinate.h

Index: Source/core/rendering/style/GridCoordinate.h
diff --git a/Source/core/rendering/style/GridCoordinate.h b/Source/core/rendering/style/GridCoordinate.h
index 951c259c5eebada5ec8772bc287ddba4fd09ee7c..fa78aa22a790fda21adf457637e385b2a7d3d6b0 100644
--- a/Source/core/rendering/style/GridCoordinate.h
+++ b/Source/core/rendering/style/GridCoordinate.h
@@ -114,6 +114,11 @@ struct GridSpan {
         return resolvedInitialPosition == o.resolvedInitialPosition && resolvedFinalPosition == o.resolvedFinalPosition;
     }
 
+    size_t integerSpan() const
+    {
+        return resolvedFinalPosition.toInt() - resolvedInitialPosition.toInt() + 1;
+    }
+
     GridResolvedPosition resolvedInitialPosition;
     GridResolvedPosition resolvedFinalPosition;