Change Process.start to return a future that completes with a

tests/standalone/io/process_stdout_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.
 //
 // VMOptions=
 // VMOptions=--short_socket_read
 // VMOptions=--short_socket_write
 // VMOptions=--short_socket_read --short_socket_write
 
 #import("dart:io");
 #import("dart:math");
 
 #source("process_test_util.dart");
 
-void test(Process process, int expectedExitCode) {
-  // Wait for the process to start and then interact with it.
-  process.onStart = () {
+void test(Future<Process> future, int expectedExitCode) {
+  future.then((process) {
+    process.onExit = (exitCode) {
+      Expect.equals(expectedExitCode, exitCode);
+    };
+
     List<int> data = "ABCDEFGHI\n".charCodes();
     final int dataSize = data.length;
 
     InputStream input = process.stdout;
     OutputStream output = process.stdin;
 
     int received = 0;
     List<int> buffer = [];
 
     void readData() {
@@ skipping 13 matching lines @@
           process.close();
         } else if (received === dataSize) {
           process.close();
         }
       }
     }
 
     output.write(data);
     output.close();
     input.onData = readData;
-  };
-
-  process.onExit = (exitCode) {
-    Expect.equals(expectedExitCode, exitCode);
-  };
+  });
 }
 
 main() {
   // Run the test using the process_test binary.
   test(Process.start(getProcessTestFileName(),
                      const ["0", "1", "99", "0"]), 99);
 
   // Run the test using the dart binary with an echo script.
   // The test runner can be run from either the root or from runtime.
   var scriptFile = new File("tests/standalone/io/process_std_io_script.dart");
   if (!scriptFile.existsSync()) {
     scriptFile = new File("../tests/standalone/io/process_std_io_script.dart");
   }
   Expect.isTrue(scriptFile.existsSync());
   test(Process.start(new Options().executable, [scriptFile.name, "0"]), 0);
 }