Make it possible to change BottomAppBar's border radius

[ndonkoHenri]

Implement ClipRRect

Working Flutter Example

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: HomeScreen(),
    );
  }
}

class HomeScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Text("Content goes here"),
      ),
      bottomNavigationBar: ClipRRect(
        borderRadius: BorderRadius.only(
          topLeft: Radius.circular(30),
          topRight: Radius.circular(30),
        ),
        child: BottomAppBar(
          color: Colors.blue,
          child: Row(
            mainAxisAlignment: MainAxisAlignment.spaceAround,
            children: <Widget>[
              IconButton(
                icon: Icon(Icons.home, color: Colors.white),
                onPressed: () {},
              ),
            ],
          ),
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {},
        child: Icon(Icons.add),
      ),
    );
  }
}

Discussed in #4285