Repository: flutter
Issue: [mobile]  Selected DropdownMenuItem isn't highlighted on mobile only
Labels: c: regression,platform-android,platform-ios,framework,f: material design,f: focus,has reproducible steps,P2,found in release: 3.3,found in release: 3.7,team-design,triaged-design

## Steps to Reproduce
1. Run the code following on the mobile simulator or physical mobile device 

<details> 
<summary>code sample</summary> 

```dart
/// Flutter code sample for DropdownButton
// @dart = 2.9

// This sample shows a `DropdownButton` with a large arrow icon,
// purple text style, and bold purple underline, whose value is one of "One",
// "Two", "Free", or "Four".
//
// ![](https://flutter.github.io/assets-for-api-docs/assets/material/dropdown_button.png)

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

/// This is the main application widget.
class MyApp extends StatelessWidget {
  static const String _title = 'Flutter Code Sample';

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: _title,
      home: Scaffold(
        appBar: AppBar(title: const Text(_title)),
        body: Center(
          child: MyStatefulWidget(),
        ),
      ),
    );
  }
}

/// This is the stateful widget that the main application instantiates.
class MyStatefulWidget extends StatefulWidget {
  MyStatefulWidget({Key key}) : super(key: key);

  @override
  _MyStatefulWidgetState createState() => _MyStatefulWidgetState();
}

/// This is the private State class that goes with MyStatefulWidget.
class _MyStatefulWidgetState extends State<MyStatefulWidget> {
  String dropdownValue = 'One';

  @override
  Widget build(BuildContext context) {
    return DropdownButton<String>(
      value: dropdownValue,
      icon: Icon(Icons.arrow_downward),
      iconSize: 24,
      elevation: 16,
      style: TextStyle(color: Colors.deepPurple),
      underline: Container(
        height: 2,
        color: Colors.deepPurpleAccent,
      ),
      onChanged: (String newValue) {
        setState(() {
          dropdownValue = newValue;
        });
      },
      items: <String>[
        'One',
        'Two',
        'Free',
        'Four',
        'Five',
        'Six',
        'Seven',
        'Eight',
        'Nine',
        'Ten',
        'Eleven',
        'Twelve',
        'Thirteen',
        'Fourteen',
        'Fifteen',
        'Sixteen',
        'Eighteen',
        'Nineteen',
        'Twenty',
        'Twenty One',
        'Twenty Two',
        'Twenty Three',
        'Twenty Four',
        'Twenty Five'
      ].map<DropdownMenuItem<String>>((String value) {
        return DropdownMenuItem<String>(
          value: value,
          child: Text(value),
        );
      }).toList(),
    );
  }
}

```

</details> 

2. Select an item and then close the dropdown menu, open it again, selected isn't highlighted

### Preview

| Mobile | Web & Desktop |
| --------------- | --------------- |
![ezgif com-gif-maker (2)](https://user-images.githubusercontent.com/48603081/98830078-fbcde580-245f-11eb-8590-68b4967c8bb2.gif) | ![ezgif com-gif-maker (3)](https://user-images.githubusercontent.com/48603081/98830110-06887a80-2460-11eb-91e3-9672b4d7dd69.gif)




### Additional context:
1. Selected item is correctly highlighted on the web and desktop using the same code sample. 
2. Issue reproduced on `stable`, `beta`, `master`

<details> 
<summary>flutter doctor -v</summary> 

```bash
[✓] Flutter (Channel stable, 1.22.3, on Mac OS X 10.15.7 19H15, locale en-GB)
    • Flutter version 1.22.3 at /Users/tahatesser/Code/flutter_stable
    • Framework revision 8874f21e79 (13 days ago), 2020-10-29 14:14:35 -0700
    • Engine revision a1440ca392
    • Dart version 2.10.3

 
[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.2)
    • Android SDK at /Users/tahatesser/Code/sdk
    • Platform android-30, build-tools 30.0.2
    • ANDROID_HOME = /Users/tahatesser/Code/sdk
    • 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-b3-6915495)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 12.2)
    • Xcode at /Volumes/SanDisk/Xcode-beta.app/Contents/Developer
    • Xcode 12.2, Build version 12B5044c
    • CocoaPods version 1.10.0

[!] Android Studio (version 4.1)
    • Android Studio at /Applications/Android Studio.app/Contents
    ✗ Flutter plugin not installed; this adds Flutter specific functionality.
    ✗ Dart plugin not installed; this adds Dart specific functionality.
    • Java version OpenJDK Runtime Environment (build
      1.8.0_242-release-1644-b3-6915495)

[✓] VS Code (version 1.51.0)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.16.0

[✓] Connected device (2 available)
    • RMX2001 (mobile)     • EUYTFEUSQSRGDA6D          • android-arm64 • Android 10
      (API 29)
    • Taha’s iPad (mobile) • 00008020-000255113EE8402E • ios           • iOS 14.2

! Doctor found issues in 1 category.
```

```bash
[✓] Flutter (Channel beta, 1.23.0-18.1.pre, on Mac OS X 10.15.7 19H15 x86_64, locale
    en-GB)
    • Flutter version 1.23.0-18.1.pre at /Users/tahatesser/Code/flutter_beta
    • Framework revision 198df796aa (4 weeks ago), 2020-10-15 12:04:33 -0700
    • Engine revision 1d12d82d9c
    • Dart version 2.11.0 (build 2.11.0-213.1.beta)

 
[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.2)
    • Android SDK at /Users/tahatesser/Code/sdk
    • Platform android-30, build-tools 30.0.2
    • ANDROID_HOME = /Users/tahatesser/Code/sdk
    • 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-b3-6915495)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 12.2)
    • Xcode at /Volumes/SanDisk/Xcode-beta.app/Contents/Developer
    • Xcode 12.2, Build version 12B5044c
    • CocoaPods version 1.10.0

[✓] Chrome - develop for the web
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Android Studio (version 4.1)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build
      1.8.0_242-release-1644-b3-6915495)

[✓] VS Code (version 1.51.0)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.16.0

[✓] Connected device (5 available)
    • RMX2001 (mobile)     • EUYTFEUSQSRGDA6D                     • android-arm64  •
      Android 10 (API 29)
    • Taha’s iPad (mobile) • 00008020-000255113EE8402E            • ios            •
      iOS 14.2
    • iPhone 11 (mobile)   • FF1F0A30-1571-44C9-B79D-E18CE0622B1B • ios            •
      com.apple.CoreSimulator.SimRuntime.iOS-14-2 (simulator)
    • Web Server (web)     • web-server                           • web-javascript •
      Flutter Tools
    • Chrome (web)         • chrome                               • web-javascript •
      Google Chrome 86.0.4240.193

• No issues found!
```

```bash
[✓] Flutter (Channel master, 1.24.0-8.0.pre.194, on Mac OS X 10.15.7 19H15
    darwin-x64, locale en-GB)
    • Flutter version 1.24.0-8.0.pre.194 at /Users/tahatesser/Code/flutter_master
    • Framework revision 018467cdb1 (8 hours ago), 2020-11-11 02:04:03 -0500
    • Engine revision 81f219c59c
    • Dart version 2.12.0 (build 2.12.0-31.0.dev)

[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.2)
    • Android SDK at /Users/tahatesser/Code/sdk
    • Platform android-30, build-tools 30.0.2
    • ANDROID_HOME = /Users/tahatesser/Code/sdk
    • 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-b3-6915495)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 12.2)
    • Xcode at /Volumes/SanDisk/Xcode-beta.app/Contents/Developer
    • Xcode 12.2, Build version 12B5044c
    • CocoaPods version 1.10.0

[✓] Chrome - develop for the web
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Android Studio (version 4.1)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build
      1.8.0_242-release-1644-b3-6915495)

[✓] VS Code (version 1.51.0)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.16.0

[✓] Connected device (6 available)
    • RMX2001 (mobile)     • EUYTFEUSQSRGDA6D                     • android-arm64  •
      Android 10 (API 29)
    • Taha’s iPad (mobile) • 00008020-000255113EE8402E            • ios            •
      iOS 14.2
    • iPhone 11 (mobile)   • FF1F0A30-1571-44C9-B79D-E18CE0622B1B • ios            •
      com.apple.CoreSimulator.SimRuntime.iOS-14-2 (simulator)
    • macOS (desktop)      • macos                                • darwin-x64     •
      Mac OS X 10.15.7 19H15 darwin-x64
    • Web Server (web)     • web-server                           • web-javascript •
      Flutter Tools
    • Chrome (web)         • chrome                               • web-javascript •
      Google Chrome 86.0.4240.193

• No issues found!
```

</details>