[CSS Grid Layout] Update grid-auto-flow to the new syntax

LayoutTests/fast/css-grid-layout/resources/grid.css

 .grid {
     display: grid;
     background-color: grey;
 }
 
 .indefiniteSizeGrid {
     display: grid;
     background-color: grey;
     width: -webkit-min-content;
     height: auto;
@@ skipping 105 matching lines @@
     grid-row: auto;
 }
 
 .autoRowThirdColumn {
     background-color: magenta;
     grid-column: 3;
     grid-row: auto;
 }
 
 /* Grid element flow. */
-.gridAutoFlowNone {
-    grid-auto-flow: none;
+.gridAutoFlowStack {
+    grid-auto-flow: stack;
 }
 
 .gridAutoFlowColumn {
     grid-auto-flow: column;
 }
 
 .gridAutoFlowRow {
     grid-auto-flow: row;
 }
 
@@ skipping 23 matching lines @@
     -webkit-writing-mode: vertical-lr;
 }
 
 .horizontalBT {
     -webkit-writing-mode: horizontal-bt;
 }
 
 .directionRTL {
     direction: rtl;
 }