[Gallery] Fix directory structure (#312)

gallery/lib/studies/shrine/page_status.dart

@@ -0,0 +1,52 @@
+// 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/material.dart';
+
+import 'package:gallery/layout/adaptive.dart';
+
+class PageStatus extends InheritedWidget {
+  const PageStatus({
+    Key key,
+    @required this.cartController,
+    @required this.menuController,
+    @required Widget child,
+  })  : assert(cartController != null),
+        assert(menuController != null),
+        super(key: key, child: child);
+
+  final AnimationController cartController;
+  final AnimationController menuController;
+
+  static PageStatus of(BuildContext context) {
+    return context.dependOnInheritedWidgetOfExactType<PageStatus>();
+  }
+
+  @override
+  bool updateShouldNotify(PageStatus old) =>
+      old.cartController != cartController ||
+      old.menuController != menuController;
+}
+
+bool productPageIsVisible(BuildContext context) {
+  return _cartControllerOf(context).isDismissed &&
+      (_menuControllerOf(context).isCompleted || isDisplayDesktop(context));
+}
+
+bool menuPageIsVisible(BuildContext context) {
+  return _cartControllerOf(context).isDismissed &&
+      (_menuControllerOf(context).isDismissed || isDisplayDesktop(context));
+}
+
+bool cartPageIsVisible(BuildContext context) {
+  return _cartControllerOf(context).isCompleted;
+}
+
+AnimationController _cartControllerOf(BuildContext context) {
+  return PageStatus.of(context).cartController;
+}
+
+AnimationController _menuControllerOf(BuildContext context) {
+  return PageStatus.of(context).menuController;
+}