Add Cupertino to gallery and add CupertinoButton and many yak friends (#8411)

* Add cupertino to gallery and add CupertinoButto

* Use single quotes

* Add disabled state

* Some review notes

* Make button animation more responsive and tweak timing

* Renamed things Cupertino

* Button with background, move cupertino demos, move material demos

* Move 2 level list too

* Refactor various demo route names

* Some review notes

* More reviews and add test

* Linter as

* Move private constant up

examples/flutter_gallery/lib/demo/material/cards_demo.dart

diff --git a/examples/flutter_gallery/lib/demo/material/cards_demo.dart b/examples/flutter_gallery/lib/demo/material/cards_demo.dart
new file mode 100644
index 0000000..cba2d80
--- /dev/null
+++ b/examples/flutter_gallery/lib/demo/material/cards_demo.dart
@@ -0,0 +1,149 @@
+// Copyright 2016 The Chromium Authors. 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 TravelDestination {
+  const TravelDestination({ this.assetName, this.title, this.description });
+
+  final String assetName;
+  final String title;
+  final List<String> description;
+
+  bool get isValid => assetName != null && title != null && description?.length == 3;
+}
+
+final List<TravelDestination> destinations = <TravelDestination>[
+  const TravelDestination(
+    assetName: 'packages/flutter_gallery_assets/top_10_australian_beaches.jpg',
+    title: 'Top 10 Australian beaches',
+    description: const <String>[
+      'Number 10',
+      'Whitehaven Beach',
+      'Whitsunday Island, Whitsunday Islands',
+    ],
+  ),
+  const TravelDestination(
+    assetName: 'packages/flutter_gallery_assets/kangaroo_valley_safari.jpg',
+    title: 'Kangaroo Valley Safari',
+    description: const <String>[
+      '2031 Moss Vale Road',
+      'Kangaroo Valley 2577',
+      'New South Wales',
+    ],
+  )
+];
+
+class TravelDestinationItem extends StatelessWidget {
+  TravelDestinationItem({ Key key, this.destination }) : super(key: key) {
+    assert(destination != null && destination.isValid);
+  }
+
+  static final double height = 328.0;
+  final TravelDestination destination;
+
+  @override
+  Widget build(BuildContext context) {
+    ThemeData theme = Theme.of(context);
+    TextStyle titleStyle = theme.textTheme.headline.copyWith(color: Colors.white);
+    TextStyle descriptionStyle = theme.textTheme.subhead;
+
+    return new SizedBox(
+      height: height,
+      child: new Card(
+        child: new Column(
+          crossAxisAlignment: CrossAxisAlignment.start,
+          children: <Widget>[
+            // photo and title
+            new SizedBox(
+              height: 184.0,
+              child: new Stack(
+                children: <Widget>[
+                  new Positioned.fill(
+                    child: new Image.asset(
+                      destination.assetName,
+                      fit: ImageFit.cover,
+                    ),
+                  ),
+                  new Positioned(
+                    bottom: 16.0,
+                    left: 16.0,
+                    right: 16.0,
+                    child: new FittedBox(
+                      fit: ImageFit.scaleDown,
+                      alignment: FractionalOffset.centerLeft,
+                      child: new Text(destination.title,
+                        style: titleStyle,
+                      ),
+                    ),
+                  ),
+                ],
+              ),
+            ),
+            // description and share/expore buttons
+            new Expanded(
+              child: new Padding(
+                padding: const EdgeInsets.fromLTRB(16.0, 16.0, 16.0, 0.0),
+                child: new DefaultTextStyle(
+                  softWrap: false,
+                  overflow: TextOverflow.ellipsis,
+                  style: descriptionStyle,
+                  child: new Column(
+                    crossAxisAlignment: CrossAxisAlignment.start,
+                    children: <Widget>[
+                      // three line description
+                      new Text(destination.description[0]),
+                      new Text(destination.description[1]),
+                      new Text(destination.description[2]),
+                    ],
+                  ),
+                ),
+              ),
+            ),
+            // share, explore buttons
+            // TODO(abarth): The theme and the bar should be part of card.
+            new ButtonTheme.bar(
+              child: new ButtonBar(
+                alignment: MainAxisAlignment.start,
+                children: <Widget>[
+                  new FlatButton(
+                    child: new Text('SHARE'),
+                    onPressed: () { /* do nothing */ },
+                  ),
+                  new FlatButton(
+                    child: new Text('EXPLORE'),
+                    onPressed: () { /* do nothing */ },
+                  ),
+                ],
+              ),
+            ),
+          ],
+        ),
+      ),
+    );
+  }
+}
+
+class CardsDemo extends StatelessWidget {
+  static const String routeName = '/material/cards';
+
+  @override
+  Widget build(BuildContext context) {
+    return new Scaffold(
+      appBar: new AppBar(
+        title: new Text('Travel stream')
+      ),
+      body: new ListView(
+        itemExtent: TravelDestinationItem.height,
+        padding: const EdgeInsets.only(top: 8.0, left: 8.0, right: 8.0),
+        children: destinations.map((TravelDestination destination) {
+          return new Container(
+            margin: const EdgeInsets.only(bottom: 8.0),
+            child: new TravelDestinationItem(destination: destination)
+          );
+        }).toList()
+      )
+    );
+  }
+}