add stderr to log processor for desktop (#31874)

packages/flutter_tools/lib/src/desktop.dart

@@ -53,17 +53,21 @@ Future<bool> killProcess(String executable) async {
 }
 
 class DesktopLogReader extends DeviceLogReader {
-  final StreamController<String> _inputController = StreamController<String>.broadcast();
+  final StreamController<List<int>> _inputController = StreamController<List<int>>.broadcast();
 
   void initializeProcess(Process process) {
-    _inputController.addStream(process.stdout
-      .transform(utf8.decoder)
-      .transform(const LineSplitter()));
+    process.stdout.listen(_inputController.add);
+    process.stderr.listen(_inputController.add);
+    process.exitCode.then((int result) {
+      _inputController.close();
+    });
   }
 
   @override
   Stream<String> get logLines {
-    return _inputController.stream;
+    return _inputController.stream
+      .transform(utf8.decoder)
+      .transform(const LineSplitter());
   }
 
   @override

packages/flutter_tools/test/macos/macos_device_test.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:async';
 import 'dart:convert';
 
 import 'package:file/memory.dart';
@@ -20,6 +21,7 @@ import 'package:flutter_tools/src/macos/macos_device.dart';
 
 import '../src/common.dart';
 import '../src/context.dart';
+import '../src/mocks.dart';
 
 void main() {
   group(MacOSDevice, () {
@@ -69,21 +71,21 @@ tester    17193   0.0  0.2  4791128  37820   ??  S     2:27PM   0:00.09 /Applica
       final MockFileSystem mockFileSystem = MockFileSystem();
       final MockProcessManager mockProcessManager = MockProcessManager();
       final MockFile mockFile = MockFile();
-      final MockProcess mockProcess = MockProcess();
       when(macOSApp.executable(any)).thenReturn('test');
       when(mockFileSystem.file('test')).thenReturn(mockFile);
       when(mockFile.existsSync()).thenReturn(true);
       when(mockProcessManager.start(<String>['test'])).thenAnswer((Invocation invocation) async {
-        return mockProcess;
+        return FakeProcess(
+          exitCode: Completer<int>().future,
+          stdout: Stream<List<int>>.fromIterable(<List<int>>[
+            utf8.encode('Observatory listening on http://127.0.0.1/0\n'),
+          ]),
+          stderr: const Stream<List<int>>.empty(),
+        );
       });
       when(mockProcessManager.run(any)).thenAnswer((Invocation invocation) async {
         return ProcessResult(0, 1, '', '');
       });
-      when(mockProcess.stdout).thenAnswer((Invocation invocation) {
-        return Stream<List<int>>.fromIterable(<List<int>>[
-          utf8.encode('Observatory listening on http://127.0.0.1/0'),
-        ]);
-      });
 
       testUsingContext('Can run from prebuilt application', () async {
         final LaunchResult result = await device.startApp(macOSApp, prebuiltApplication: true);