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

tests/standalone/io/process_environment_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.
 
 #import('dart:io');
 #import('dart:isolate');
 #source('process_test_util.dart');
 
 runEnvironmentProcess(Map environment, name, callback) {
   var dartExecutable = new Options().executable;
   var options = new ProcessOptions();
   options.environment = environment;
   var printEnv = 'tests/standalone/io/print_env.dart';
   if (!new File(printEnv).existsSync()) {
     printEnv = '../$printEnv';
   }
-  var process = new Process.run(dartExecutable,
-                                [printEnv, name],
-                                options,
-                                (exit, out, err) {
-    Expect.equals(0, exit);
-    callback(out);
+  Process.run(dartExecutable, [printEnv, name], options).then((result) {
+    Expect.equals(0, result.exitCode);
+    callback(result.stdout);
   });
-  process.onError = (e) => Expect.fail("Unexpected process start error: '$e'");
 }
 
 testEnvironment() {
   var donePort = new ReceivePort();
   Map env = Platform.environment;
   Expect.isFalse(env.isEmpty());
   // Check that some value in the environment stays the same when passed
   // to another process.
   for (var k in env.getKeys()) {
     runEnvironmentProcess(env, k, (output) {
@@ skipping 13 matching lines @@
     });
     // Only check one value to not spin up too many processes testing the
     // same things.
     break;
   }
 }
 
 main() {
   testEnvironment();
 }