Add an iOS app clip sample (#538)

ios_app_clip/lib/main.dart

@@ -0,0 +1,54 @@
+// Copyright 2020 The Flutter team. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:device_info/device_info.dart';
+import 'package:flutter/cupertino.dart';
+import 'package:flutter/material.dart';
+
+void main() {
+  runApp(Demo());
+}
+
+// The same content is shown for both the main app target and in the App
+// Clip.
+class Demo extends StatefulWidget {
+  @override
+  State<StatefulWidget> createState() => _DemoState();
+}
+
+class _DemoState extends State<Demo> {
+  String deviceInfo = '';
+
+  @override
+  void initState() {
+    DeviceInfoPlugin().iosInfo.then((IosDeviceInfo info) {
+      setState(() {
+        deviceInfo = '${info.name} on ${info.systemName} version '
+            '${info.systemVersion}';
+      });
+    });
+    super.initState();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return CupertinoApp(
+      home: CupertinoPageScaffold(
+        navigationBar: CupertinoNavigationBar(
+          middle: Text('App Clip'),
+        ),
+        child: Center(
+          child: Column(
+            mainAxisAlignment: MainAxisAlignment.center,
+            children: <Widget>[
+              Text(deviceInfo),
+              Padding(padding: EdgeInsets.only(top: 18)),
+              FlutterLogo(size: 128),
+            ],
+          ),
+        ),
+      ),
+    );
+  }
+}