We're getting warnings in our test runs that the request for listWorkers is running while shutting down. We can prevent these unnecessary calls from running by passing the list of workers running down from the workerListChanged event

Error: Connection closed, pending request to server0.conn0.child2/frameTarget1, type listWorkers failed
   Request stack:
     request devtools/shared/protocol/Front.js 256:14
     generateRequestMethods/</frontProto[name] devtools/shared/protocol/Front/FrontClassWithSpec.js 47:19
     listWorkerTargets devtools/client/debugger/src/client/firefox/targets.js 118:36
     updateTargets devtools/client/debugger/src/client/firefox/targets.js 191:25
     fetchThreads devtools/client/debugger/src/client/firefox/commands.js 432:36
     updateThreads/< devtools/client/debugger/src/actions/threads.js 97:34
     thunk/</</< devtools/client/debugger/src/actions/utils/middleware/thunk.js 29:45
     bindActionCreator/< devtools/client/shared/vendor/redux.js 520:12
     threadListChanged devtools/client/debugger/src/client/firefox/events.js 141:11
     _emit devtools/shared/event-emitter.js 226:34
     emit devtools/shared/event-emitter.js 172:18
     emit devtools/shared/event-emitter.js 324:18
     onPacket devtools/shared/protocol/Front.js 294:13
     onPacket devtools/client/devtools-client.js 493:13
     send/< devtools/shared/transport/local-transport.js 68:25
     exports.makeInfallible/< devtools/shared/ThreadSafeDevToolsUtils.js 103:22
     DevToolsUtils.executeSoon*exports.executeSoon devtools/shared/DevToolsUtils.js 47:21
     send devtools/shared/transport/local-transport.js 56:21
     send devtools/server/devtools-server-connection.js 91:20
     onWorkerListChanged devtools/server/actors/root.js 450:15
     _notifyListChanged devtools/server/actors/worker/worker-target-actor-list.js 184:10
     onUnregister devtools/server/actors/worker/worker-target-actor-list.js 200:12
   " {file: "resource://devtools/shared/protocol/Front.js" line: 77}]

This patch shows what that would look like.

One concern I have is that this event would now be async, but i think that is okay

Tracking Fission DevTools bugs for Fission Nightly (M6) milestone

If possible we should invest into bug 1593940 rather than polishing this code which we know will be removed by that other bug.
Does it break anything, or is it only test warnings?

If that's test warning, this should be removed from the MVP list.

Tracking dt-fission-m2-mvp bugs for Fission Nightly milestone (M6c)

Jason: question for you in comment 2

Agreed.