[Gallery] Fix directory structure (#312)

gallery/lib/studies/shrine/supplemental/layout_cache.dart

@@ -0,0 +1,22 @@
+// 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';
+
+class LayoutCache extends InheritedWidget {
+  const LayoutCache({
+    Key key,
+    @required this.layouts,
+    @required Widget child,
+  }) : super(key: key, child: child);
+
+  static Map<String, List<List<int>>> of(BuildContext context) {
+    return context.dependOnInheritedWidgetOfExactType<LayoutCache>().layouts;
+  }
+
+  final Map<String, List<List<int>>> layouts;
+
+  @override
+  bool updateShouldNotify(LayoutCache old) => true;
+}