Call setState() (#21642)

packages/flutter/lib/src/material/chip.dart

diff --git a/packages/flutter/lib/src/material/chip.dart b/packages/flutter/lib/src/material/chip.dart
index 4dc9a15..3510e9f 100644
--- a/packages/flutter/lib/src/material/chip.dart
+++ b/packages/flutter/lib/src/material/chip.dart
@@ -677,7 +677,9 @@
 ///             label: Text('Item $index'),
 ///             selected: _value == index,
 ///             onSelected: (bool selected) {
-///               _value = selected ? index : null;
+///               setState(() {
+///                 _value = selected ? index : null;
+///               });
 ///             },
 ///           );
 ///         },