Dart: Adds optional named arguments for creating bindings.

examples/dart/hello_world/hello/main.dart

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // To run this app:
 // mojo_shell mojo:hello
 
 import 'mojo:application';
 import 'mojo:bindings';
 import 'mojo:core';
 
 class Hello extends Application {
   Hello.fromHandle(MojoHandle handle) : super.fromHandle(handle);
 
   void initialize(List<String> args, String url) {
     print("$url Hello");
     // We expect to find the world mojo application at the same
     // path as this application.
-    connectToApplication(url.replaceAll("hello", "world"));
-    close();
+    var c = connectToApplication(url.replaceAll("hello", "world"));
+    c.listen(onClosed: close);

[hansmuller1, 2015/03/03 20:32:16]

I like this.  It's subtly different from the original, since before we
unconditionally closed the hello app. Since this is an example, you might
include a comment about waiting for the world app to close, and then closing
this app.

[zra, 2015/03/03 21:28:54]

Added comment.

   }
 }
 
 main(List args) {
   MojoHandle appHandle = new MojoHandle(args[0]);
   new Hello.fromHandle(appHandle);
 }