Resume testing message extraction on Windows after dart:io fix

pkg/intl/test/message_extraction/message_extraction_test.dart

Index: pkg/intl/test/message_extraction/message_extraction_test.dart
diff --git a/pkg/intl/test/message_extraction/message_extraction_test.dart b/pkg/intl/test/message_extraction/message_extraction_test.dart
index a040df1d5991b98841627d3af0ead43eab8b207e..e472cdaed51b4e5bad91c27c6bfda3aa0050f80e 100644
--- a/pkg/intl/test/message_extraction/message_extraction_test.dart
+++ b/pkg/intl/test/message_extraction/message_extraction_test.dart
@@ -7,6 +7,7 @@ library message_extraction_test;
 import 'package:unittest/unittest.dart';
 import 'dart:io';
 import 'dart:async';
+import 'dart:convert';
 import 'package:path/path.dart' as path;
 import '../data_directory.dart';
 
@@ -74,7 +75,8 @@ Future<ProcessResult> run(ProcessResult previousResult, List<String> filenames)
       ..add(filesInTheRightDirectory.first)
       ..addAll(["--output-dir=${dir()}"])
       ..addAll(filesInTheRightDirectory.skip(1));
-  var result = Process.run(dart, args);
+  var result = Process.run(dart, args, stdoutEncoding: UTF8,
+      stderrEncoding: UTF8);
   return result;
 }