Close stdout and stderr before terminating the VM.

pkg/unittest/lib/vm_config.dart

Index: pkg/unittest/lib/vm_config.dart
diff --git a/pkg/unittest/lib/vm_config.dart b/pkg/unittest/lib/vm_config.dart
index d8b3f2308c591f2acaa0774c353e67ee2a4d53a7..7ff2154f628deb6a13c8ccf84956c10c58b55e0a 100644
--- a/pkg/unittest/lib/vm_config.dart
+++ b/pkg/unittest/lib/vm_config.dart
@@ -7,6 +7,7 @@
  */
 library unittest_vm_config;
 
+import 'dart:async';
 import 'dart:io';
 import 'unittest.dart';
 
@@ -38,14 +39,18 @@ class VMConfiguration extends Configuration {
   }
 
   void onDone(bool success) {
+    int status;
     try {
       super.onDone(success);
-      exit(0);
+      status = 0;
     } catch (ex) {
       // A non-zero exit code is used by the test infrastructure to detect
       // failure.
-      exit(1);
+      status = 1;
     }
+    Future.wait([stdout.close(), stderr.close()]).then((_) {
+      exit(status);
+    });
   }
 }