Add support for starting a detached process

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.
+//
+// VMOptions=
+// VMOptions=--short_socket_read
+// VMOptions=--short_socket_write
+// VMOptions=--short_socket_read --short_socket_write

[kustermann, 2015/01/16 16:11:04]

Since we don't do any I/O here, I don't think we need to make 5 different test
cases out of this one.

[Søren Gjesse, 2015/01/21 12:32:35]

Good point. Removed.

+
+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], detached: true);
+  future.then((process) {
+    print(process.pid);

[Lasse Reichstein Nielsen, 2015/01/15 09:55:40]

Expect.isNotNull(process.pid);
?

[Søren Gjesse, 2015/01/21 12:32:35]

Done added

Expect.isTrue(process.pid is int);

as well.

+    Expect.isNull(process.exitCode);
+    Expect.isNull(process.stderr);
+    Expect.isNull(process.stdin);
+    Expect.isNull(process.stdout);
+    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'], detached: true);
+    future.then((process) {
+      Expect.fail('Starting process from invalid executable succeeded');
+    }).catchError((e) {
+      Expect.isTrue(e is ProcessException);

[Lasse Reichstein Nielsen, 2015/01/15 09:55:40]

Won't this catch the expect.fail from above (but then it'll fail, so I guess the
test is still correctly failing, just with a different error than expected).
Consider changing to:
   future.then((process) {
     Expect.fail('Starting process from invalid executable succeeded');
   }, onError: (e) {
     Expect.isTrue(e is ProcessException);
   }).whenComplete( ...

[Søren Gjesse, 2015/01/21 12:32:35]

Good catch, thanks!

+    }).whenComplete(() {
+      temp.deleteSync();
+      asyncEnd();
+    });
+  });
+}
+
+main() {
+  test();
+  testFailure();
+}