How to "Set Value..." when debugging with Flutter in Android Studio

Problem

The following image and code are the defaults when creating Flutter App with "New Flutter Project".

  import 'package:flutter/material.dart';

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

  class MyApp extends StatelessWidget {

    @override
    Widget build(BuildContext context) {
      return new MaterialApp(
        title: 'Flutter Demo',
        theme: new ThemeData(

          primarySwatch: Colors.blue,
        ),
        home: new MyHomePage(title: 'Flutter Demo Home Page'),
      );
    }
  }

  class MyHomePage extends StatefulWidget {
    MyHomePage({Key key, this.title}) : super(key: key);

    final String title;

    @override
    _MyHomePageState createState() => new _MyHomePageState();
  }

  class _MyHomePageState extends State<MyHomePage> {
    int _counter = 0;

    void _incrementCounter() {
      setState(() {

        _counter++; // <- I set a breakpoint

      });
    }

    @override
    Widget build(BuildContext context) {

      return new Scaffold(
        appBar: new AppBar(

          title: new Text(widget.title),
        ),
        body: new Center(

          child: new Column(

            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              new Text(
                'You have pushed the button this many times:',
              ),
              new Text(
                '$_counter',
                style: Theme.of(context).textTheme.display1,
              ),
            ],
          ),
        ),
        floatingActionButton: new FloatingActionButton(
          onPressed: _incrementCounter,
          tooltip: 'Increment',
          child: new Icon(Icons.add),
        ), // This trailing comma makes auto-formatting nicer for build methods.
      );
    }
  }

I attempted to "Set Value..." by putting a break point in the code where _counter is incremented when debugging with this code, but can not be pressed even if I hover the cursor.

①　"Debug 'main.dart' (^D)" ②　Breakpoint ③　"Set Value..."

Question

• How to "Set Value..." when debugging with Flutter in Android Studio.

Development Environment

• Android Studio 3.1.4
• Flutter 0.5.1
• Dart 2
• Android SDK built for x86

Best regards,