Add segmented control to gallery (#19192)

* Adding segmented control to gallery

examples/flutter_gallery/lib/demo/cupertino/cupertino.dart

@@ -8,5 +8,6 @@ export 'cupertino_dialog_demo.dart';
 export 'cupertino_navigation_demo.dart';
 export 'cupertino_picker_demo.dart';
 export 'cupertino_refresh_demo.dart';
+export 'cupertino_segmented_control_demo.dart';
 export 'cupertino_slider_demo.dart';
 export 'cupertino_switch_demo.dart';

examples/flutter_gallery/lib/demo/cupertino/cupertino_segmented_control_demo.dart

+// Copyright 2018 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/cupertino.dart';
+import 'package:flutter/material.dart';
+
+const Color _kKeyUmbraOpacity = const Color(0x33000000); // alpha = 0.2
+const Color _kKeyPenumbraOpacity = const Color(0x24000000); // alpha = 0.14
+const Color _kAmbientShadowOpacity = const Color(0x1F000000); // alpha = 0.12
+
+class CupertinoSegmentedControlDemo extends StatefulWidget {
+  static const String routeName = 'cupertino/segmented_control';
+
+  @override
+  _CupertinoSegmentedControlDemoState createState() => new _CupertinoSegmentedControlDemoState();
+}
+
+class _CupertinoSegmentedControlDemoState extends State<CupertinoSegmentedControlDemo> {
+  final Map<int, Widget> children = const <int, Widget>{
+    0: Center(
+      child: const Text('Midnight'),
+    ),
+    1: Center(
+      child: const Text('Viridian'),
+    ),
+    2: Center(
+      child: const Text('Cerulean'),
+    ),
+  };
+
+  final Map<int, Widget> icons = const <int, Widget>{
+    0: Center(
+      child: const FlutterLogo(
+        colors: Colors.indigo,
+        size: 200.0,
+      ),
+    ),
+    1: Center(
+      child: const FlutterLogo(
+        colors: Colors.teal,
+        size: 200.0,
+      ),
+    ),
+    2: Center(
+      child: const FlutterLogo(
+        colors: Colors.cyan,
+        size: 200.0,
+      ),
+    ),
+  };
+
+  int sharedValue = 0;
+
+  @override
+  Widget build(BuildContext context) {
+    return new Scaffold(
+      appBar: new AppBar(
+        title: const Text('Cupertino Segmented Control'),
+      ),
+      body: new Column(
+        children: <Widget>[
+          const Padding(
+            padding: const EdgeInsets.all(16.0),
+          ),
+          new SegmentedControl<int>(
+            children: children,
+            onValueChanged: (int newValue) {
+              setState(() {
+                sharedValue = newValue;
+              });
+            },
+            groupValue: sharedValue,
+          ),
+          new Expanded(
+            child: new Padding(
+              padding: const EdgeInsets.symmetric(
+                vertical: 32.0,
+                horizontal: 16.0,
+              ),
+              child: new Container(
+                  padding: const EdgeInsets.symmetric(
+                    vertical: 64.0,
+                    horizontal: 16.0,
+                  ),
+                  decoration: new BoxDecoration(
+                    color: CupertinoColors.white,
+                    borderRadius: new BorderRadius.circular(3.0),
+                    boxShadow: const <BoxShadow>[
+                      const BoxShadow(
+                        offset: const Offset(0.0, 3.0),
+                        blurRadius: 5.0,
+                        spreadRadius: -1.0,
+                        color: _kKeyUmbraOpacity,
+                      ),
+                      const BoxShadow(
+                        offset: const Offset(0.0, 6.0),
+                        blurRadius: 10.0,
+                        spreadRadius: 0.0,
+                        color: _kKeyPenumbraOpacity,
+                      ),
+                      const BoxShadow(
+                        offset: const Offset(0.0, 1.0),
+                        blurRadius: 18.0,
+                        spreadRadius: 0.0,
+                        color: _kAmbientShadowOpacity,
+                      ),
+                    ],
+                  ),
+                  child: icons[sharedValue]),
+            ),
+          ),
+        ],
+      ),
+    );
+  }
+}

examples/flutter_gallery/lib/gallery/demos.dart

@@ -421,6 +421,13 @@ List<GalleryDemo> _buildGalleryDemos() {
       routeName: CupertinoRefreshControlDemo.routeName,
       buildRoute: (BuildContext context) => new CupertinoRefreshControlDemo(),
     ),
+    new GalleryDemo(
+      title: 'Segmented Control',
+      icon: GalleryIcons.tabs,
+      category: _kCupertinoComponents,
+      routeName: CupertinoSegmentedControlDemo.routeName,
+      buildRoute: (BuildContext context) => new CupertinoSegmentedControlDemo(),
+    ),
     new GalleryDemo(
       title: 'Sliders',
       icon: GalleryIcons.sliders,