Fix widget.dart to work with the latest web_ui library. Specifically, query selectors need to use "…

test/effects/swapper_tests.dart

Index: test/effects/swapper_tests.dart
diff --git a/test/effects/swapper_tests.dart b/test/effects/swapper_tests.dart
index 51fa238744be17b00730cc5c5c30604bdb125398..b13436496e7183aa1da76dab0f7dff0ac57bde83 100644
--- a/test/effects/swapper_tests.dart
+++ b/test/effects/swapper_tests.dart
@@ -110,7 +110,7 @@ void _swapperTest(int childCount,
             expect(displayedIndicies.length, 1, reason: 'there should only be one displayed item');
             expect(displayedIndicies[0], expectedDisplayed);
           }
-        }), onError: (AsyncError error) {
+        }), onError: (error) {
           registerException(error.error, error.stackTrace);
         });
     }