Repository: flutter
Issue: When use CupertinoPageScaffold in showCupertinoModalPopup without navigationBar，the button at the top does not work
Labels: platform-ios,framework,f: cupertino,has reproducible steps,found in release: 3.3,found in release: 3.5,team-design,triaged-design


flutter doctor -v
```
[✓] Flutter (Channel stable, 1.20.2, on Mac OS X 10.15.5 19F101, locale
    zh-Hans-CN)
    • Flutter version 1.20.2 at /Users/limi/Desktop/flutter
    • Framework revision bbfbf1770c (6 weeks ago), 2020-08-13 08:33:09 -0700
    • Engine revision 9d5b21729f
    • Dart version 2.9.1
    • Pub download mirror https://pub.flutter-io.cn
    • Flutter download mirror https://storage.flutter-io.cn

 
[✓] Android toolchain - develop for Android devices (Android SDK version 29.0.3)
    • Android SDK at /Users/limi/Library/Android/sdk
    • Platform android-29, build-tools 29.0.3
    • Java binary at: /Applications/Android
      Studio.app/Contents/jre/jdk/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build
      1.8.0_242-release-1644-b3-6222593)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 11.3)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Xcode 11.3, Build version 11C29
    • CocoaPods version 1.9.1

[✓] Android Studio (version 4.0)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin version 48.1.2
    • Dart plugin version 193.7547
    • Java version OpenJDK Runtime Environment (build
      1.8.0_242-release-1644-b3-6222593)

[✓] Connected device (2 available)
    • iPhone X (mobile)  • E192D7AA-0C14-42AA-9123-3093588AE267 • ios •
      com.apple.CoreSimulator.SimRuntime.iOS-13-3 (simulator)
    • iPhone 11 (mobile) • BC00638F-639B-48DA-A925-EBFF088EC216 • ios •
      com.apple.CoreSimulator.SimRuntime.iOS-13-3 (simulator)

• No issues found!
```
Code
```
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return CupertinoApp(
      title: 'Flutter Demo',
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

   void _show() {
    showCupertinoModalPopup(context: context, builder: (_) => CupertinoPageScaffold(
      child: Container(
        color: Colors.white,
        width: double.infinity,
        height: 300,
        child: Row(
          crossAxisAlignment: CrossAxisAlignment.start,
          mainAxisAlignment: MainAxisAlignment.end,
          children: [
            CupertinoButton(
                minSize: 0,
                padding: EdgeInsets.zero,
                color: Colors.red,
                child: Icon(Icons.close),
                onPressed: () {
                  print('close');
                  Navigator.of(context).pop();
                }
            ),
          ],
        ),
      ),
    ));
  }

  @override
  Widget build(BuildContext context) {
    return CupertinoPageScaffold(
      child: Stack(
        children: [
          Center(
            child: CupertinoButton(
              child: Text('Dialog'),
              onPressed: _show,
            ),
          )
        ],
      ),
    );
  }
}
```

1. Click the dialog button to show a dialog
2. Click the close button to close the dialog, it does not work