add AnimatedBuilder demo

lib/my_app_meta.dart

@@ -8,6 +8,7 @@ import 'package:provider/provider.dart';
 import './my_route.dart';
 import './routes/about.dart';
 
+import './routes/animation_animated_builder_ex.dart';
 import './routes/animation_animated_widget_ex.dart';
 import './routes/animation_basic_ex.dart';
 import './routes/animation_hero_ex.dart';
@@ -175,6 +176,7 @@ const kMyAppRoutesStructure = <MyRouteGroup>[
       HeroExample(),
       BasicAnimationExample(),
       AnimatedWidgetExample(),
+      AnimatedBuilderExample(),
     ],
   ),
   MyRouteGroup(

lib/routes/animation_animated_builder_ex.dart

@@ -0,0 +1,79 @@
+import 'dart:math';
+
+import 'package:flutter/material.dart';
+import '../my_route.dart';
+
+class AnimatedBuilderExample extends MyRoute {
+  const AnimatedBuilderExample(
+      [String sourceFile = 'lib/routes/animation_animated_builder_ex.dart'])
+      : super(sourceFile);
+
+  @override
+  get title => 'AnimatedBuilder';
+
+  @override
+  get description => 'Similar to AnimatedWidget.';
+
+  @override
+  get links => {
+        'Tutorial':
+            'https://flutter.dev/docs/development/ui/animations/tutorial#refactoring-with-animatedbuilder',
+        'Widget of the Week (YouTube)': 'https://youtu.be/N-RiyZlv8v8',
+      };
+
+  @override
+  Widget buildMyRouteContent(BuildContext context) {
+    return new _AnimatedBuilderDemo();
+  }
+}
+
+class _AnimatedBuilderDemo extends StatefulWidget {
+  @override
+  _AnimatedBuilderDemoState createState() => _AnimatedBuilderDemoState();
+}
+
+class _AnimatedBuilderDemoState extends State<_AnimatedBuilderDemo>
+    with SingleTickerProviderStateMixin {
+  AnimationController _controller;
+
+  @override
+  void initState() {
+    super.initState();
+    this._controller =
+        AnimationController(duration: Duration(seconds: 1), vsync: this);
+  }
+
+  @override
+  void dispose() {
+    super.dispose();
+    this._controller.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final rotateAnimation =
+        Tween<double>(begin: 0, end: pi).animate(this._controller);
+    return Column(
+      children: <Widget>[
+        AnimatedBuilder(
+          animation: rotateAnimation,
+          child: FlutterLogo(size: 72.0),
+          builder: (context, child) {
+            return Transform.rotate(
+              angle: rotateAnimation.value,
+              child: child,
+            );
+          },
+        ),
+        RaisedButton(
+          child: Text('Forward animation'),
+          onPressed: () => _controller.forward(),
+        ),
+        RaisedButton(
+          child: Text('Reverse animation'),
+          onPressed: () => _controller.reverse(),
+        ),
+      ],
+    );
+  }
+}