Add support for starting a detached process

tests/standalone/io/process_detached_script.dart

Index: tests/standalone/io/process_detached_script.dart
diff --git a/tools/canary.dart b/tests/standalone/io/process_detached_script.dart
similarity index 63%
copy from tools/canary.dart
copy to tests/standalone/io/process_detached_script.dart
index cca1f90cd7be8eb2481a00a89bbc7ba7edaa6d4f..122831b433b2d6ef75f6b028643abc49ca0db6ef 100644
--- a/tools/canary.dart
+++ b/tests/standalone/io/process_detached_script.dart
@@ -1,11 +1,11 @@
 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+//
+// Simple script hanging for testing a detached process.
 
-// Script which exits with code 42.
+import 'dart:isolate';
 
-import 'dart:io';
-
-void main() {
-  exitCode = 42;
+main() {
+  new ReceivePort().listen(print);
 }