Add an option for starting a detached process with stdio connected

tests/standalone/io/process_detached_test.dart

 // 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.
 //
 // Process test program to test detached processes.
 
 import 'dart:async';
 import 'dart:io';
 
 import "package:async_helper/async_helper.dart";
 import "package:expect/expect.dart";
 
 import "process_test_util.dart";
 
 void test() {
   asyncStart();
   var script =
       Platform.script.resolve('process_detached_script.dart').toFilePath();
-  var future = Process.start(Platform.executable, [script], detach: true);
+  var future = Process.start(
+      Platform.executable, [script], mode: ProcessStartMode.DETACHED);
   future.then((process) {
-    print(process.pid);
     Expect.isNotNull(process.pid);
     Expect.isTrue(process.pid is int);
     Expect.isNull(process.exitCode);
     Expect.isNull(process.stderr);
     Expect.isNull(process.stdin);
     Expect.isNull(process.stdout);
     Expect.isTrue(process.kill());
   }).whenComplete(() {
     asyncEnd();
   });
 }
 
+void testWithStdio() {
+  asyncStart();
+  var script =
+      Platform.script.resolve('process_detached_script.dart').toFilePath();
+  var future = Process.start(
+      Platform.executable,
+      [script, 'echo'],
+      mode: ProcessStartMode.DETACHED_WITH_STDIO);
+  future.then((process) {
+    Expect.isNotNull(process.pid);
+    Expect.isTrue(process.pid is int);
+    Expect.isNull(process.exitCode);
+    var message = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
+    process.stdin.add(message);
+    process.stdin.close();
+    var f1 = process.stdout.fold([], (p, e) => p..addAll(e));
+    var f2 = process.stderr.fold([], (p, e) => p..addAll(e));
+    Future.wait([f1, f2])
+        .then((values) {
+          Expect.listEquals(values[0], message);
+          Expect.listEquals(values[1], message);
+        })
+        .whenComplete(() {
+          Expect.isTrue(process.kill());
+        });
+  }).whenComplete(() {
+    asyncEnd();
+  });
+}
+
 void testFailure() {
   asyncStart();
   Directory.systemTemp.createTemp('dart_detached_process').then((temp) {
-    var future = Process.start(temp.path, ['a', 'b'], detach: true);
+    var future = Process.start(
+        temp.path, ['a', 'b'], mode: ProcessStartMode.DETACHED);
     future.then((process) {
       Expect.fail('Starting process from invalid executable succeeded');
     }, onError: (e) {
       Expect.isTrue(e is ProcessException);
     }).whenComplete(() {
       temp.deleteSync();
       asyncEnd();
     });
   });
 }
 
 main() {
   test();
+  testWithStdio();
   testFailure();
 }