How to obtain Flutter Engine Unit Test Coverage on Android

### Steps to reproduce

I can run Flutter Engine Unit Test on Android through such a command:
`./testing/run_tests.py --type android --android-variant android_debug_arm64`
but how to obtain unit test coverage? It seems that --coverage is not supported on the android platform.

### Expected results

I can obtain the Flutter Engine Unit Test Coverage on Android

### Actual results

It seems Flutter Engine Unit Test Coverage not support on Android

### Code sample

Code sample

```dart
[Paste your code here]
```

### Screenshots or Video

Screenshots / Video demonstration

[Upload media here]

### Logs

Logs

```console
[Paste your logs here]
```

### Flutter Doctor output

Doctor output

```console
[Paste your output here]
```