Clean up PollingDeviceDiscovery dispose (#59709)

packages/flutter_tools/lib/src/commands/daemon.dart

@@ -179,10 +179,10 @@ class Daemon {
 
   void _send(Map<String, dynamic> map) => sendCommand(map);
 
-  void shutdown({ dynamic error }) {
-    _commandSubscription?.cancel();
+  Future<void> shutdown({ dynamic error }) async {
+    await _commandSubscription?.cancel();
     for (final Domain domain in _domainMap.values) {
-      domain.dispose();
+      await domain.dispose();
     }
     if (!_onExitCompleter.isCompleted) {
       if (error == null) {
@@ -273,7 +273,7 @@ abstract class Domain {
     return val as int;
   }
 
-  void dispose() { }
+  Future<void> dispose() async { }
 }
 
 /// This domain responds to methods like [version] and [shutdown].
@@ -351,8 +351,8 @@ class DaemonDomain extends Domain {
   }
 
   @override
-  void dispose() {
-    _subscription?.cancel();
+  Future<void> dispose() async {
+    await _subscription?.cancel();
   }
 
   /// Enumerates the platforms supported by the provided project.
@@ -828,9 +828,9 @@ class DeviceDomain extends Domain {
   }
 
   @override
-  void dispose() {
+  Future<void> dispose() async {
     for (final PollingDeviceDiscovery discoverer in _discoverers) {
-      discoverer.dispose();
+      await discoverer.dispose();
     }
   }
 

packages/flutter_tools/lib/src/device.dart

@@ -352,7 +352,7 @@ abstract class PollingDeviceDiscovery extends DeviceDiscovery {
     return deviceNotifier.onRemoved;
   }
 
-  void dispose() => stopPolling();
+  Future<void> dispose() async => await stopPolling();
 
   @override
   String toString() => '$name device discovery';

packages/flutter_tools/lib/src/ios/devices.dart

@@ -43,11 +43,6 @@ class IOSDevices extends PollingDeviceDiscovery {
        _logger = logger ?? globals.logger,
        super('iOS devices');
 
-  @override
-  void dispose() {
-    _observedDeviceEventsSubscription?.cancel();
-  }
-
   final Platform _platform;
   final XCDevice _xcdevice;
   final IOSWorkflow _iosWorkflow;

packages/flutter_tools/test/general.shard/ios/devices_test.dart

@@ -482,6 +482,28 @@ void main() {
       expect(rescheduledStream.hasListener, isFalse);
     });
 
+    testWithoutContext('dispose cancels polling subscription', () async {
+      final IOSDevices iosDevices = IOSDevices(
+        platform: macPlatform,
+        xcdevice: mockXcdevice,
+        iosWorkflow: mockIosWorkflow,
+        logger: logger,
+      );
+      when(mockXcdevice.isInstalled).thenReturn(true);
+      when(mockXcdevice.getAvailableIOSDevices())
+          .thenAnswer((Invocation invocation) => Future<List<IOSDevice>>.value(<IOSDevice>[]));
+
+      final StreamController<Map<XCDeviceEvent, String>> eventStream = StreamController<Map<XCDeviceEvent, String>>();
+      when(mockXcdevice.observedDeviceEvents()).thenAnswer((_) => eventStream.stream);
+
+      await iosDevices.startPolling();
+      expect(iosDevices.deviceNotifier.items, isEmpty);
+      expect(eventStream.hasListener, isTrue);
+
+      await iosDevices.dispose();
+      expect(eventStream.hasListener, isFalse);
+    });
+
     final List<Platform> unsupportedPlatforms = <Platform>[linuxPlatform, windowsPlatform];
     for (final Platform unsupportedPlatform in unsupportedPlatforms) {
       testWithoutContext('pollingGetDevices throws Unsupported Operation exception on ${unsupportedPlatform.operatingSystem}', () async {