[Gallery] Fix directory structure (#312)

gallery/lib/demos/cupertino/cupertino_navigation_bar_demo.dart

@@ -0,0 +1,82 @@
+// 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 'package:flutter/cupertino.dart';
+import 'package:flutter/material.dart';
+import 'package:gallery/l10n/gallery_localizations.dart';
+
+// BEGIN cupertinoNavigationBarDemo
+
+class CupertinoNavigationBarDemo extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) {
+    return Navigator(onGenerateRoute: (settings) {
+      return _NoAnimationCupertinoPageRoute<void>(
+        title: GalleryLocalizations.of(context).demoCupertinoNavigationBarTitle,
+        builder: (context) => CupertinoPageScaffold(
+          child: CustomScrollView(
+            slivers: [
+              CupertinoSliverNavigationBar(
+                automaticallyImplyLeading: false,
+              ),
+              SliverPadding(
+                padding: MediaQuery.of(context)
+                    .removePadding(removeTop: true)
+                    .padding,
+                sliver: SliverList(
+                  delegate: SliverChildBuilderDelegate(
+                    (context, index) {
+                      final title = GalleryLocalizations.of(context)
+                          .starterAppDrawerItem(index + 1);
+                      return ListTile(
+                        onTap: () {
+                          Navigator.of(context).push(CupertinoPageRoute<void>(
+                            title: title,
+                            builder: (context) => _SecondPage(),
+                          ));
+                        },
+                        title: Text(title),
+                      );
+                    },
+                    childCount: 20,
+                  ),
+                ),
+              ),
+            ],
+          ),
+        ),
+      );
+    });
+  }
+}
+
+class _SecondPage extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) {
+    return CupertinoPageScaffold(
+      navigationBar: const CupertinoNavigationBar(),
+      child: Container(),
+    );
+  }
+}
+
+/// A CupertinoPageRoute without any transition animations.
+class _NoAnimationCupertinoPageRoute<T> extends CupertinoPageRoute<T> {
+  _NoAnimationCupertinoPageRoute({
+    @required WidgetBuilder builder,
+    String title,
+  }) : super(builder: builder, title: title);
+
+  @override
+  Widget buildTransitions(
+    BuildContext context,
+    Animation<double> animation,
+    Animation<double> secondaryAnimation,
+    Widget child,
+  ) {
+    return child;
+  }
+}
+
+// END