Change dart:io to use Future for one-shot operations.

tests/standalone/io/process_exit_test.dart

 // Copyright (c) 2012, 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 process communication.
 
 #library("ProcessExitTest");
 #import("dart:io");
 #source("process_test_util.dart");
 
 testExit() {
-  Process process = new Process.start(getProcessTestFileName(),
-                                      const ["0", "0", "99", "0"]);
+  InteractiveProcess process = Process.start(getProcessTestFileName(),
+                                             const ["0", "0", "99", "0"]);
 
   process.onExit = (int exitCode) {
     Expect.equals(exitCode, 99);
     process.close();
   };
 }
 
 testExitRun() {
-  Process process = new Process.run(getProcessTestFileName(),
-                                    const ["0", "0", "99", "0"],
-                                    null,
-                                    (exit, out, err) {
-    Expect.equals(exit, 99);
-    Expect.equals(out, '');
-    Expect.equals(err, '');
+  Process.run(getProcessTestFileName(),
+              const ["0", "0", "99", "0"]).then((result) {
+    Expect.equals(result.exitCode, 99);
+    Expect.equals(result.stdout, '');
+    Expect.equals(result.stderr, '');
   });
 }
 
 main() {
   testExit();
   testExitRun();
 }