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

LayoutTests/fast/css-grid-layout/place-cell-by-index.html

Index: LayoutTests/fast/css-grid-layout/place-cell-by-index.html
diff --git a/LayoutTests/fast/css-grid-layout/place-cell-by-index.html b/LayoutTests/fast/css-grid-layout/place-cell-by-index.html
index 67b9e970c7bf7e0b2747ca6bfec25b2bbb64ef59..3ef0b6ab0156878bb88f41c105da5705eb5f337a 100644
--- a/LayoutTests/fast/css-grid-layout/place-cell-by-index.html
+++ b/LayoutTests/fast/css-grid-layout/place-cell-by-index.html
@@ -7,8 +7,8 @@ if (window.testRunner)
 <link href="resources/grid.css" rel="stylesheet">
 <style>
 .grid {
-    grid-columns: 50px 60px;
-    grid-rows: 20px 30px;
+    grid-definition-columns: 50px 60px;
+    grid-definition-rows: 20px 30px;
     max-width: 110px;
 }