Migrate desktop_photo_search to top level (#1002)

desktop_photo_search/material/lib/src/widgets/unsplash_notice.dart

@@ -0,0 +1,107 @@
+// Copyright 2022 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:flutter/gestures.dart';
+import 'package:flutter/material.dart';
+import 'package:url_launcher/url_launcher.dart';
+
+import '../../unsplash_access_key.dart';
+
+final _unsplashHomepage =
+    'https://unsplash.com/?utm_source=${Uri.encodeFull(unsplashAppName)}&utm_medium=referral';
+final _unsplashPrivacyPolicy =
+    'https://unsplash.com/privacy?utm_source=${Uri.encodeFull(unsplashAppName)}&utm_medium=referral';
+
+class UnsplashNotice extends StatefulWidget {
+  const UnsplashNotice({Key? key, required this.child}) : super(key: key);
+  final Widget child;
+
+  @override
+  State<UnsplashNotice> createState() => _UnsplashNoticeState();
+}
+
+class _UnsplashNoticeState extends State<UnsplashNotice> {
+  bool noticeAccepted = false;
+
+  @override
+  void initState() {
+    super.initState();
+    WidgetsBinding.instance!.addPostFrameCallback((timeStamp) {
+      showDialog<void>(
+          barrierDismissible: false,
+          context: context,
+          builder: (context) {
+            return _UnsplashDialog(accepted: () {
+              setState(() {
+                noticeAccepted = true;
+              });
+            });
+          });
+    });
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return widget.child;
+  }
+}
+
+class _UnsplashDialog extends StatelessWidget {
+  const _UnsplashDialog({Key? key, required this.accepted}) : super(key: key);
+  final Function accepted;
+
+  @override
+  Widget build(BuildContext context) {
+    return AlertDialog(
+      title: const Text('Unsplash Notice'),
+      content: RichText(
+        text: TextSpan(
+            text: 'This is a sample desktop application provided by Google'
+                ' that enables you to search ',
+            style: const TextStyle(color: Colors.grey),
+            children: [
+              TextSpan(
+                text: 'Unsplash',
+                recognizer: TapGestureRecognizer()
+                  ..onTap = () async {
+                    if (!await launch(_unsplashHomepage)) {
+                      throw 'Could not launch $_unsplashHomepage';
+                    }
+                  },
+                style: const TextStyle(color: Colors.blue),
+              ),
+              const TextSpan(
+                text: ' for photographs that interest you. When you search'
+                    ' for and interact with photos, Unsplash will collect'
+                    ' information about you and your use of the Unsplash'
+                    ' services. Learn more about ',
+                style: TextStyle(color: Colors.grey),
+              ),
+              TextSpan(
+                text: 'how Unsplash collects and uses data',
+                recognizer: TapGestureRecognizer()
+                  ..onTap = () async {
+                    if (!await launch(_unsplashPrivacyPolicy)) {
+                      throw 'Could not launch $_unsplashPrivacyPolicy';
+                    }
+                  },
+                style: const TextStyle(color: Colors.blue),
+              ),
+              const TextSpan(
+                text: '.',
+                style: TextStyle(color: Colors.grey),
+              ),
+            ]),
+      ),
+      actions: [
+        TextButton(
+            child: const Text('GOT IT'),
+            onPressed: () {
+              accepted();
+              Navigator.pop(context);
+            })
+      ],
+    );
+  }
+}