Adding shrine. (#3)

Adds a new version of Shrine from the MDC codelabs.

shrine/lib/home.dart

@@ -0,0 +1,35 @@
+// Copyright 2018-present the Flutter authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import 'package:flutter/material.dart';
+import 'package:scoped_model/scoped_model.dart';
+
+import 'model/app_state_model.dart';
+import 'model/product.dart';
+import 'supplemental/asymmetric_view.dart';
+
+class HomePage extends StatelessWidget {
+  final Category category;
+
+  const HomePage({this.category: Category.all});
+
+  @override
+  Widget build(BuildContext context) {
+    return ScopedModelDescendant<AppStateModel>(
+      builder: (context, child, model) => AsymmetricView(
+            products: model.getProducts(),
+          ),
+    );
+  }
+}