Repository: flutter
Issue: Translucent Flutter Screen glitches on Application Resume
Labels: platform-android,engine,has reproducible steps,P2,found in release: 2.0,found in release: 2.3,team-android,triaged-android

https://user-images.githubusercontent.com/10841769/117787685-44ccee00-b279-11eb-91db-878c4ddc1856.mp4

When the app goes back to the background and back again, the transparency of the background color is lost！

Here is jump code with translucent！

<details> 
<summary>code snippet</summary> 

```dart
currentActivity.startActivity(
                        FlutterActivity
                                .withNewEngine()
                                .initialRoute(url)
                                .backgroundMode(FlutterActivityLaunchConfigs.BackgroundMode.transparent)
                                .build(currentActivity)
                );
```

Here is widget

```dart
class SecondPage extends StatefulWidget {
  SecondPage({Map params}) {
    print("second page params:$params");
  }

  @override
  SecondState createState() {
    return new SecondState();
  }
}

class SecondState extends State<SecondPage> {

  @override
  Widget build(BuildContext context) {
    final size = MediaQuery.of(context).size;
    return Scaffold(
      backgroundColor: Colors.red.withAlpha(127),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          crossAxisAlignment: CrossAxisAlignment.center,
          children: <Widget>[
            Container(
              width: size.width - 40,
              height: 300,
              color: Colors.amber,
              alignment: Alignment.center,
              child: const Text(
                '这是透明容器内的Flutter内容,包括：\n\n1.半透明背景\n2.黄色内容展示区\n3.下方按钮',
                style: TextStyle(
                  fontSize: 16,
                  decoration: TextDecoration.none,
                ),
              ),
            ),
            const SizedBox(height: 30),
            Container(
              width: 150,
              height: 44,
              color: Colors.blue,
              alignment: Alignment.center,
              child: FlatButton(
                onPressed: () => Vdn.close(),
                child: const Text(
                  '关闭透明容器',
                  style: TextStyle(
                      fontSize: 16,
                      decoration: TextDecoration.none,
                      color: Colors.white),
                ),
              ),
            ),
            const SizedBox(height: 30),
            Container(
              width: 180,
              height: 44,
              color: Colors.blue,
              alignment: Alignment.center,
              child: FlatButton(
                onPressed: () => Vdn.goToPage('/third').then((value) => print(value)),
                child: const Text(
                  '透明容器内跳转页面',
                  style: TextStyle(
                      fontSize: 16,
                      decoration: TextDecoration.none,
                      color: Colors.white),
                ),
              ),
            ),
          ],
        ),
      ),
    );
  }
}
```

</details>

Here is flutter doctor


<details> 
<summary>flutter doctor</summary> 
	
```console
Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel unknown, 2.0.6, on macOS 11.2.3 20D91 darwin-x64, locale
    zh-Hans-CN)
[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.3)
[!] Xcode - develop for iOS and macOS
    ✗ CocoaPods installed but not working.
        You appear to have CocoaPods installed but it is not working.
        This can happen if the version of Ruby that CocoaPods was installed with
        is different from the one being used to invoke it.
        This can usually be fixed by re-installing CocoaPods.
      To re-install see
      https://guides.cocoapods.org/using/getting-started.html#installation for
      instructions.
[✓] Chrome - develop for the web
[✓] Android Studio (version 4.1)
[✓] VS Code (version 1.54.3)
[✓] Connected device (2 available)
```

</details>