Examples: move markAsLaidOut() to just before the return, so the asserts work

sky/examples/style/block-layout.sky

Index: sky/examples/style/block-layout.sky
diff --git a/sky/examples/style/block-layout.sky b/sky/examples/style/block-layout.sky
index a707af0e54a430c0a11509ce52ac31da6c650ae8..7076685fb39d84466fe44c66871230c542c6be4f 100644
--- a/sky/examples/style/block-layout.sky
+++ b/sky/examples/style/block-layout.sky
@@ -7,7 +7,6 @@ SKY MODULE
 <script>
  module.exports.BlockLayoutManager = class BlockLayoutManager extends sky.LayoutManager {
    function layout(width, height) {
-     this.markAsLaidOut();
      if (width == null)
        width = this.getIntrinsicWidth().value;
      let autoHeight = false;
@@ -31,11 +30,15 @@ SKY MODULE
      }
      if (autoHeight)
        height = y;
+     this.markAsLaidOut();
      return {
        width: width,
        height: height,
      }
    }
+   function layoutDescendants() {
+     this.layout(node.width, node.height);
+   }
    function getIntrinsicWidth() {
      let width = this.node.getProperty('width');
      if (typeof width != 'number') {