[CSS Grid Layout] overflow-position keyword for align and justify properties.

Source/core/css/resolver/StyleAdjuster.cpp

Index: Source/core/css/resolver/StyleAdjuster.cpp
diff --git a/Source/core/css/resolver/StyleAdjuster.cpp b/Source/core/css/resolver/StyleAdjuster.cpp
index dc278e60be6e74766c7a3126440e13ee641804c2..af83723536ebb0cfdb4eca4d7137bbd33acd9624 100644
--- a/Source/core/css/resolver/StyleAdjuster.cpp
+++ b/Source/core/css/resolver/StyleAdjuster.cpp
@@ -250,6 +250,12 @@ void StyleAdjuster::adjustStyleForAlignment(RenderStyle& style, const RenderStyl
     bool isFlexOrGrid = style.isDisplayFlexibleOrGridBox();
     bool absolutePositioned = style.position() == AbsolutePosition;
 
+    // The default overflow alignment is 'true' for flex or grid items/contaners, 'safe' otherwise.
+    if (style.justifyItemsOverflowAlignment() == OverflowAlignmentDefault)
+        style.setJustifyItemsOverflowAlignment(isFlexOrGrid ? OverflowAlignmentTrue : OverflowAlignmentSafe);
+    if (style.justifySelfOverflowAlignment() == OverflowAlignmentDefault)
+        style.setJustifySelfOverflowAlignment(isFlexOrGrid ? OverflowAlignmentTrue : OverflowAlignmentSafe);
+
     // If the inherited value of justify-items includes the legacy keyword, 'auto'
     // computes to the the inherited value.
     // Otherwise, auto computes to: