devtools can only access the first created engine when you have multiple engines in add to app

[AshishSingh2001]

Overview

When you have a add-to-app with multiple flutter engines active at the same time, the devtools takes the first valid isolate and sets it as main, making it impossible to use widget inspector and other tools

Minimal Example App - https://github.com/AshishSingh2001/minimal-add-to-app

Steps to reproduce

• run the android app

cd android_app
./gradlew installDebug

• Attach flutter debugger to the dart VM service (you can get this from logcat)

Issue

In the debugger you will always see homeTab and don't have a way to switch to another tab

The widget inspector is build with keeping normal flutter apps in mind, where only one isolate can be the main isolate, but in add-to-app there can be multiple isolates which can render flutter separately

[AshishSingh2001]

Proposal

List down all valid isolates and allow switching between them inside settings

fetching the list of engines by adding a listener to serviceConnection.serviceManager.service?.onIsolateEvent and updating the list when the number of valid isolate's changes

[AshishSingh2001]

Came across showIsolateSelector already being used by CPU profiler and other screens which can work on all types of isolates.

For the issue raised the inspector or the performance screen won't work on all isolate but only on the isolates which have the name main and has a flutterExtension

Another way to solve this would be to have some sort of filtering mechanism exposed by the Screen to its children