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

Source/core/rendering/style/GridResolvedPosition.cpp

Index: Source/core/rendering/style/GridResolvedPosition.cpp
diff --git a/Source/core/rendering/style/GridResolvedPosition.cpp b/Source/core/rendering/style/GridResolvedPosition.cpp
index 5c7adcd2f492ee5cc6483f5eb4c89af53fbd377e..6ae9259c9f61a031a1009dc8062e601bd0950419 100644
--- a/Source/core/rendering/style/GridResolvedPosition.cpp
+++ b/Source/core/rendering/style/GridResolvedPosition.cpp
@@ -47,6 +47,12 @@ void GridResolvedPosition::initialAndFinalPositionsFromStyle(const RenderStyle&
 
     if (finalPosition.isNamedGridArea() && isNonExistentNamedLineOrArea(finalPosition.namedGridLine(), gridContainerStyle, finalPositionSide))
         finalPosition.setAutoPosition();
+
+    // If the grid item has an automatic position and a grid span for a named line in a given dimension, instead treat the grid span as one.
+    if (initialPosition.isAuto() && finalPosition.isSpan() && !finalPosition.namedGridLine().isNull())
+        finalPosition.setSpanPosition(1, String());
+    if (finalPosition.isAuto() && initialPosition.isSpan() && !initialPosition.namedGridLine().isNull())
+        initialPosition.setSpanPosition(1, String());
 }
 
 GridSpan GridResolvedPosition::resolveGridPositionsFromAutoPlacementPosition(const RenderStyle& gridContainerStyle, const RenderBox& gridItem, GridTrackSizingDirection direction, const GridResolvedPosition& resolvedInitialPosition)