[CSS Grid Layout] Rename grid-{rows|columns} to grid-definition-{rows|columns}

LayoutTests/fast/css-grid-layout/grid-element-padding-margin.html

Index: LayoutTests/fast/css-grid-layout/grid-element-padding-margin.html
diff --git a/LayoutTests/fast/css-grid-layout/grid-element-padding-margin.html b/LayoutTests/fast/css-grid-layout/grid-element-padding-margin.html
index f8538f4f2901d3d1e179ae345bee2f3c0c50aea5..af213481e384d0c13aad9aa7c89e48eb17b6ffbd 100644
--- a/LayoutTests/fast/css-grid-layout/grid-element-padding-margin.html
+++ b/LayoutTests/fast/css-grid-layout/grid-element-padding-margin.html
@@ -7,8 +7,8 @@ if (window.testRunner)
 <link href="resources/grid.css" rel="stylesheet">
 <style>
 .grid {
-    grid-columns: 100px;
-    grid-rows: 50px;
+    grid-definition-columns: 100px;
+    grid-definition-rows: 50px;
     /* Force the grid element to be shrink-to-fit. */
     position: absolute;
 }