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

tests/standalone/io/process_working_directory_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 working directory test.
 
 #library("ProcessWorkingDirectoryTest");
 #import("dart:io");
 #source("process_test_util.dart");
 
 class ProcessWorkingDirectoryTest {
   static String get fullTestFilePath {
     // Extract full path, since we run processes from another directory.
     File path = new File(getProcessTestFileName());
     Expect.isTrue(path.existsSync());
     return path.fullPathSync();
   }
 
   static void testValidDirectory() {
     Directory directory = new Directory("").createTempSync();
     Expect.isTrue(directory.existsSync());
 
     var options = new ProcessOptions();
     options.workingDirectory = directory.path;
-    Process process = Process.start(fullTestFilePath,
-                                    const ["0", "0", "99", "0"],
-                                    options);
-
-    process.onExit = (int exitCode) {
-      Expect.equals(exitCode, 99);
-      process.close();
+    var processFuture =
+        Process.start(fullTestFilePath, const ["0", "0", "99", "0"], options);
+    processFuture.then((process) {
+      process.onExit = (int exitCode) {
+        Expect.equals(exitCode, 99);
+        process.close();
+        directory.deleteSync();
+      };
+    });
+    processFuture.handleException((error) {
       directory.deleteSync();
-    };
-
-    process.onError = (error) {
-      Expect.fail("error running process $error");
-      directory.deleteSync();
-    };
+      Expect.fails("Couldn't start process");
+    });
   }
 
   static void testInvalidDirectory() {
     Directory directory = new Directory("").createTempSync();
     Expect.isTrue(directory.existsSync());
 
     var options = new ProcessOptions();
     options.workingDirectory = directory.path.concat("/subPath");
-    Process process = Process.start(fullTestFilePath,
-                                    const ["0", "0", "99", "0"],
-                                    options);
-
-    process.onExit = (int exitCode) {
+    var future = Process.start(fullTestFilePath,
+                               const ["0", "0", "99", "0"],
+                               options);
+    future.then((process) {
       Expect.fail("bad process completed");
       process.close();
       directory.deleteSync();
-    };
+    });
 
-    process.onError = (error) {
-      Expect.isNotNull(error);
+    future.handleException((e) {
+      Expect.isNotNull(e);
       directory.deleteSync();
-    };
+      return true;
+    });
   }
 }
 
 
 
 main() {
   ProcessWorkingDirectoryTest.testValidDirectory();
   ProcessWorkingDirectoryTest.testInvalidDirectory();
 }