Mojo JS Bindings: Add support for closing Proxy and Stub connections

mojo/services/public/js/shell.js

 // Copyright 2014 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.
 
 define("mojo/services/public/js/shell", [
   "mojo/public/js/bindings",
   "mojo/public/js/core",
   "mojo/public/js/connection",
   "mojo/public/interfaces/application/shell.mojom",
   "mojo/public/interfaces/application/service_provider.mojom",
@@ skipping 28 matching lines @@
     }
 
     connectToService(url, service, client) {
       return this.connectToApplication(url).requestService(service, client);
     };
 
     close() {
       this.applications_.forEach(function(application, url) {
         application.close();
       });
-      // TODO(hansmuller): Use a proper API on Proxy to close.
-      core.close(this.shellProxy.handleStash);
+      ProxyBindings(this.shellProxy).close();
       this.applications_.clear();
     }
   }
 
   var exports = {};
   exports.Shell = Shell;
   return exports;
 });