Allow opening a named pipe on MacOS and Linux.

tests/standalone/io/named_pipe_script_test.dart

+// Copyright (c) 2016, 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.
+// Testing file input stream, VM-only, standalone test.
+
+import "dart:convert";
+import "dart:io";
+
+import "package:expect/expect.dart";
+
+main() {
+  // Reading a script from a named pipe is only supported on Linux and MacOS.
+  if (!Platform.isLinux && !Platform.isMacOS) {
+    return;
+  }
+
+  final String script = 'int main() {print("Hello, World!");}';
+  final String stdinPipePath = '/dev/fd/0';
+  StringBuffer output = new StringBuffer();
+  Process.start(Platform.executable, [stdinPipePath]).then((Process process) {
+    process.stdout.transform(UTF8.decoder).listen(output.write);
+    process.stderr.transform(UTF8.decoder).listen((data) {
+      Expect.fail(data);
+    });
+    process.stdin.writeln(script);
+    process.stdin.close();
+    process.exitCode.then((int status) {
+      Expect.equals(0, status);
+      Expect.equals("Hello, World!\n", output.toString());
+    });
+  });
+}