[Gallery] Fix directory structure (#312)

gallery/lib/demos/cupertino/cupertino_refresh_demo.dart

@@ -0,0 +1,74 @@
+// Copyright 2019 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 'dart:math' show Random;
+
+import 'package:flutter/cupertino.dart';
+import 'package:flutter/material.dart';
+import 'package:gallery/l10n/gallery_localizations.dart';
+
+// BEGIN cupertinoRefreshDemo
+
+class CupertinoRefreshControlDemo extends StatefulWidget {
+  @override
+  _CupertinoRefreshControlDemoState createState() =>
+      _CupertinoRefreshControlDemoState();
+}
+
+class _CupertinoRefreshControlDemoState
+    extends State<CupertinoRefreshControlDemo> {
+  static const listCount = 20;
+  var randomList = List<int>.generate(listCount, (i) => i + 1);
+
+  void _shuffleList() => randomList.shuffle(Random());
+
+  @override
+  Widget build(BuildContext context) {
+    return CupertinoPageScaffold(
+      child: CustomScrollView(
+        // If left unspecified, the [CustomScrollView] appends an
+        // [AlwaysScrollableScrollPhysics]. Behind the scene, the ScrollableState
+        // will attach that [AlwaysScrollableScrollPhysics] to the output of
+        // [ScrollConfiguration.of] which will be a [ClampingScrollPhysics]
+        // on Android.
+        // To demonstrate the iOS behavior in this demo and to ensure that the list
+        // always scrolls, we specifically use a [BouncingScrollPhysics] combined
+        // with a [AlwaysScrollableScrollPhysics]
+        physics: const BouncingScrollPhysics(
+          parent: AlwaysScrollableScrollPhysics(),
+        ),
+        slivers: [
+          CupertinoSliverNavigationBar(
+            automaticallyImplyLeading: false,
+            largeTitle: Text(
+              GalleryLocalizations.of(context).demoCupertinoPullToRefreshTitle,
+            ),
+          ),
+          CupertinoSliverRefreshControl(
+            onRefresh: () {
+              return Future<void>.delayed(const Duration(seconds: 1))
+                ..then<void>((_) {
+                  if (mounted) {
+                    setState(() => _shuffleList());
+                  }
+                });
+            },
+          ),
+          SliverList(
+            delegate: SliverChildBuilderDelegate(
+              (context, index) {
+                final title = GalleryLocalizations.of(context)
+                    .starterAppDrawerItem(randomList[index]);
+                return ListTile(title: Text(title));
+              },
+              childCount: listCount,
+            ),
+          ),
+        ],
+      ),
+    );
+  }
+}
+
+// END