support for external download managers

app/lib/features/geckoview/features/browser/domain/services/engine_settings_replication.dart

@@ -99,6 +99,23 @@ class EngineSettingsReplicationService
       },
     );
 
+    ref.listen(
+      fireImmediately: true,
+      generalSettingsWithDefaultsProvider.select(
+        (settings) => settings.useExternalDownloadManager,
+      ),
+      (previous, next) async {
+        await _service.setUseExternalDownloadManager(next);
+      },
+      onError: (error, stackTrace) {
+        logger.e(
+          'Error listening to useExternalDownloadManager',
+          error: error,
+          stackTrace: stackTrace,
+        );
+      },
+    );
+
     ref.listen(
       fireImmediately: true,
       engineSettingsRepositoryProvider,

app/lib/features/geckoview/features/browser/domain/services/engine_settings_replication.g.dart

@@ -44,7 +44,7 @@ final class EngineSettingsReplicationServiceProvider
 }
 
 String _$engineSettingsReplicationServiceHash() =>
-    r'3e06f0c273090f9f9dfc42f2140d60ef9557f176';
+    r'7a4db374b521e592847a85cb8d2aa184be788ee4';
 
 abstract class _$EngineSettingsReplicationService extends $Notifier<void> {
   void build();