Add dart:io tests for creating a client and server in separate processes.

tests/standalone/io/socket_cross_process_test.dart

+// Copyright (c) 2013, 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.
+//
+
+import "package:expect/expect.dart";
+import 'dart:async';
+import 'dart:io';
+
+const int NUM_SERVERS = 10;
+
+void main() {
+  var args = new Options().arguments;
+  if (args.isEmpty) {
+    for (int i = 0; i < NUM_SERVERS; ++i) {
+      makeServer().then((server) {
+        runClientProcess(server.port).then((_) => server.close());
+      });
+    }
+  } else if (args[0] == 'client') {
+    int port = int.parse(args[1]);
+    runClient(port);
+  } else {
+    Expect.fail('Unknown arguments to socket_cross_process_test.dart');
+  }
+}
+
+Future makeServer() {
+  return ServerSocket.bind(InternetAddress.LOOPBACK_IP_V4, 0).then((server) {
+    server.listen((request) {
+      request.pipe(request);
+    });
+    return server;
+  });
+}
+
+Future runClientProcess(int port) {
+  return Process.run(Platform.executable,
+                     []..addAll(Platform.executableArguments)
+                       ..add(Platform.script)
+                       ..add('client')
+                       ..add(port.toString())).then((ProcessResult result) {
+    if (result.exitCode != 0 || !result.stdout.contains('SUCCESS')) {
+      print("Client failed, exit code ${result.exitCode}");
+      print("  stdout:");
+      print(result.stdout);
+      print("  stderr:");
+      print(result.stderr);
+      Expect.fail('Client subprocess exit code: ${result.exitCode}');
+    }
+  });
+}
+
+runClient(int port) {
+  Socket.connect(InternetAddress.LOOPBACK_IP_V4, port).then((connection) {
+    connection.listen((_) { }, onDone: () => print('SUCCESS'));
+    connection.close();
+  });
+}