Mojo JS Bindings: Eliminate foo$ Stub and Proxy class members

services/js/test/pingpong.js

 #!mojo:js_content_handler
 
 define("main", [
+  "mojo/public/js/bindings",
   "mojo/services/public/js/application",
   "services/js/test/pingpong_service.mojom"
-], function(application, pingPongServiceMojom) {
+], function(bindings, application, pingPongServiceMojom) {
 
+  const ProxyBindings = bindings.ProxyBindings;
+  const StubBindings = bindings.StubBindings;
   const Application = application.Application;
   const PingPongService = pingPongServiceMojom.PingPongService;
 
   class PingPongServiceImpl {
     constructor(app, client) {
       this.app = app;
       this.client = client;
     }
     ping(value) {
       this.client.pong(value + 1);
@@ skipping 25 matching lines @@
     pingTargetService(pingTargetService, count) {
       return new Promise(function(resolve) {
         var pingTargetClient = {
           pong: function(value) {
             if (value == count) {
               pingTargetService.quit();
               resolve({ok: true});
             }
           }
         };
-        pingTargetService.local$ = pingTargetClient;
+        ProxyBindings(pingTargetService).setLocalDelegate(pingTargetClient);
         for(var i = 0; i <= count; i++)
           pingTargetService.ping(i);
       });
     }
 
     // This method is only used by the GetTargetService test.
     getPingPongService(clientProxy) {
-      clientProxy.local$ = new PingPongServiceImpl(this, clientProxy);
+      ProxyBindings(clientProxy).setLocalDelegate(
+          new PingPongServiceImpl(this, clientProxy));
     }
   }
 
   class PingPong extends Application {
     acceptConnection(url, serviceProvider) {
       serviceProvider.provideService(
           PingPongService, PingPongServiceImpl.bind(null, this));
     }
   }
 
   return PingPong;
 });