Add an iOS app clip sample (#538)

ios_app_clip/test/widget_test.dart

@@ -0,0 +1,20 @@
+// This is a basic Flutter widget test.
+//
+// To perform an interaction with a widget in your test, use the WidgetTester
+// utility that Flutter provides. For example, you can send tap and scroll
+// gestures. You can also use WidgetTester to find child widgets in the widget
+// tree, read text, and verify that the values of widget properties are correct.
+
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import 'package:ios_app_clip/main.dart';
+
+void main() {
+  testWidgets('Smoke test', (WidgetTester tester) async {
+    // Build our app and trigger a frame.
+    await tester.pumpWidget(Demo());
+
+    expect(find.byType(FlutterLogo), findsOneWidget);
+  });
+}