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

samples/leap/leap_server.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');
 
 class Conversation {
   HttpRequest request;
   HttpResponse response;
 
@@ skipping 25 matching lines @@
   }
 
   handle() {
     String path = request.path;
     if (path == '/') return redirect('/$landingPage');
     if (path == '/favicon.ico') {
       path = '/lib/dartdoc/static/favicon.ico';
     }
     if (path.contains('..') || path.contains('%')) return notFound();
     var f = new File("./$path");
-    f.exists((bool exists) {
+    f.exists().then((bool exists) {
       if (!exists) return notFound();
       if (path.endsWith('.dart')) {
         response.headers.add(HttpHeaders.CONTENT_TYPE, "application/dart");
       } else if (path.endsWith('.ico')) {
         response.headers.add(HttpHeaders.CONTENT_TYPE, "image/x-icon");
       }
       f.openInputStream().pipe(response.outputStream);
       onClosed();
     });
   }
 
   static onRequest(HttpRequest request, HttpResponse response) {
     new Conversation(request, response).handle();
   }
 }
 
 main() {
   List<String> arguments = new Options().arguments;
   if (arguments.length > 0) {
     Conversation.landingPage = arguments[0];
   }
   var server = new HttpServer();
   var host = '127.0.0.1';
   var port = 8080;
   server.listen(host, port);
   print('HTTP server started on http://$host:$port/');
   server.defaultRequestHandler = Conversation.onRequest;
 }