[animations] new animation sample: Hero Animation Demo (#364)

animations/lib/src/misc/hero_animation.dart

@@ -0,0 +1,60 @@
+// 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 HeroAnimationDemo extends StatelessWidget {
+  static const String routeName = '/misc/hero_animation';
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(),
+      body: GestureDetector(
+        child: Hero(
+          tag: 'hero-page-child',
+          child: _createHeroContainer(
+            size: 50.0,
+            color: Colors.grey[300],
+          ),
+        ),
+        onTap: () => Navigator.of(context)
+            .push<void>(MaterialPageRoute(builder: (context) => HeroPage())),
+      ),
+    );
+  }
+}
+
+class HeroPage extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      backgroundColor: Colors.lightBlue,
+      appBar: AppBar(),
+      body: Center(
+        child: Hero(
+          tag: 'hero-page-child',
+          child: _createHeroContainer(
+            size: 100.0,
+            color: Colors.white,
+          ),
+        ),
+      ),
+    );
+  }
+}
+
+StatelessWidget _createHeroContainer({double size, Color color}) {
+  return Container(
+    height: size,
+    width: size,
+    padding: EdgeInsets.all(10.0),
+    margin: size < 100.0 ? EdgeInsets.all(10.0) : EdgeInsets.all(0),
+    decoration: BoxDecoration(
+      shape: BoxShape.circle,
+      color: color,
+    ),
+    child: FlutterLogo(),
+  );
+}