use the <> icon to show code examples in the gallery (#20705)

diff --git a/examples/flutter_gallery/lib/gallery/demo.dart b/examples/flutter_gallery/lib/gallery/demo.dart
index 38de327..40424a6 100644
--- a/examples/flutter_gallery/lib/gallery/demo.dart
+++ b/examples/flutter_gallery/lib/gallery/demo.dart
@@ -64,7 +64,7 @@
               new Builder(
                 builder: (BuildContext context) {
                   return new IconButton(
-                    icon: const Icon(Icons.description),
+                    icon: const Icon(Icons.code),
                     tooltip: 'Show example code',
                     onPressed: () {
                       _showExampleCode(context);