Not sure if the event will bubble up to the parent widget and trigger
the animation with all the nested widgets and callbacks.

In the Original files,

Pressing on a grandchild widget(e.g. FlatButton) of a BackWidget it
will trigger a ModalDialog call and pressing the button will make an
async call. The Flip Effect will take place at the end of a successful
async call.

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';


void main() {
  runApp(new MaterialApp(
      home: new Container(color: Colors.white,child: new RootWidget())));
}

class RootWidget extends StatelessWidget {
  FlipWidget mainFlipWidget;

  @override
  Widget build(BuildContext context) {
    mainFlipWidget = new FlipWidget(
      frontWidget: frontWidget,backWidget: new BackWidget(
        onPressedButton: () {
          _flipMainButton();
        },),);
    return new Center(child:mainFlipWidget);
  }

  _flipMainButton() {
    mainFlipWidget.doTheFlip();
  }
}

class BackWidget extends StatefulWidget {
  BackWidget({
    this.onPressedButton,});

  final VoidCallback onPressedButton;
   Widget buttonFlipWidget;
  _BackWidgetState createState() => new _BackWidgetState();
}

class _BackWidgetState extends State<BackWidget> {

  @override
  Widget build(BuildContext context) {
    widget.buttonFlipWidget = new Container(
      height: 180.0,color: Colors.grey[200],child:new FlatButton(
        onPressed: () {
          triggerCb();
        },child: new Text('Press me'),);
    return widget.buttonFlipWidget;
  }

  triggerCb() {
      widget.onPressedButton();
  }
}

class FlipWidget extends StatefulWidget {
  FlipWidget({
    @required this.frontWidget,@required this.backWidget,});

  final Widget frontWidget;
  final Widget backWidget;
  final _FlipWidgetState _state = new _FlipWidgetState();

  doTheFlip () {
    _state.doTheFlip();
  }

  _FlipWidgetState createState() => _state;
}

class _FlipWidgetState extends State<FlipWidget> with TickerProviderStateMixin {
  AnimationController _controller;
  Animation<double> _frontScale;
  Animation<double> _backScale;

  void initState() {
    super.initState();
    _controller = new AnimationController(vsync: this,duration: const Duration(milliseconds: 1500),);
    _frontScale = new Tween(
      begin: 1.0,end: 0.0,).animate(new CurvedAnimation(parent: _controller,curve: new Interval(0.0,0.5,curve: Curves.easeIn),));
    _backScale = new CurvedAnimation(
      parent: _controller,curve: new Interval(0.5,1.0,curve: Curves.eaSEOut),);
  }

  @override
  Widget build(BuildContext context) {
//    ThemeData theme = Theme.of(context);
    return new Scaffold(
      body: new Center(
        child: new Stack(
          children: [
            new AnimatedBuilder(
              child: widget.frontWidget,animation: _backScale,builder: (BuildContext context,Widget child) {
                final Matrix4 transform = new Matrix4.identity()
                  ..scale(_backScale.value,1.0);

                return new Transform(
                  transform: transform,alignment: FractionalOffset.center,child: child,);
              },new AnimatedBuilder(
                child: widget.backWidget,animation: _frontScale,Widget child) {
                  final Matrix4 transform = new Matrix4.identity()
                    ..scale(_frontScale.value,1.0);
                  return new Transform(
                    transform: transform,);
                }
            ),],);
  }

  doTheFlip() {
    setState(() {
      if (_controller.isCompleted || _controller.velocity > 0)
        _controller.reverse();
      else
        _controller.forward();
    });
  }
}

final Widget frontWidget = new Container(
  color: Colors.white,height: 180.0,child: new Column(
    children: [
      new Text("Front Side of the card")
    ],);