Combine window.setTimeout/setInterval with Timer and Timer.repeating. Also

samples/tests/samples/lib/layout/grid_layout_demo.dart

Index: samples/tests/samples/lib/layout/grid_layout_demo.dart
diff --git a/samples/tests/samples/lib/layout/grid_layout_demo.dart b/samples/tests/samples/lib/layout/grid_layout_demo.dart
index 1d6138bc6059ac2da7b59b15acc42faa94481908..580b2c89a792f15a83e52c732ba51e38f12d1b62 100644
--- a/samples/tests/samples/lib/layout/grid_layout_demo.dart
+++ b/samples/tests/samples/lib/layout/grid_layout_demo.dart
@@ -110,7 +110,7 @@ void printMetrics(String example) {
   sb.add("  verifyExample('$example', {\n");
   final children = node.children;
 
-  window.setImmediate(() {
+  window.immediate.then((_) {
     for (int i = 0; i < children.length; i++) {
       _appendMetrics(sb, children[i], '    ');
     }