Support for vetoing an attempt to pop the current route (#7488)

diff --git a/examples/flutter_gallery/test/update_test.dart b/examples/flutter_gallery/test/update_test.dart
index 184a3d8..5ab567c 100644
--- a/examples/flutter_gallery/test/update_test.dart
+++ b/examples/flutter_gallery/test/update_test.dart
@@ -33,7 +33,9 @@
     expect(backButton, findsOneWidget);
     await tester.tap(backButton);
     await tester.pump(); // Start the pop "back" operation.
+    await tester.pump(); // Complete the willPop() Future.
     await tester.pump(const Duration(seconds: 1)); // transition is complete
+    //await tester.pumpUntilNoTransientCallbacks(const Duration(seconds: 1));
 
     expect(find.text('UPDATE'), findsNothing);
   });