(Not for review) Dummy C++ side Custom Controls implementation

extensions/renderer/resources/media_router_bindings.js

 // 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.
 
 var mediaRouter;
 
 define('media_router_bindings', [
     'content/public/renderer/frame_interfaces',
+    'chrome/browser/media/router/mojo/media_controller.mojom',
     'chrome/browser/media/router/mojo/media_router.mojom',
     'extensions/common/mojo/keep_alive.mojom',
     'mojo/common/time.mojom',
     'mojo/public/js/bindings',
     'url/mojo/origin.mojom',
 ], function(frameInterfaces,
+            mediaControllerMojom,
             mediaRouterMojom,
             keepAliveMojom,
             timeMojom,
             bindings,
             originMojom) {
   'use strict';
 
   /**
    * Converts a media sink to a MediaSink Mojo object.
    * @param {!MediaSink} sink A media sink.
@@ skipping 810 matching lines @@
     // to be missing this API.
     if (!this.handlers_.searchSinks) {
       return Promise.resolve({'sink_id': ''});
     }
     this.handlers_.onBeforeInvokeHandler();
     return Promise.resolve({
       'sink_id': this.handlers_.searchSinks(sinkId, sourceUrn, searchCriteria)
     });
   };
 
+  MediaRouteProvider.prototype.createMediaRouteController = function(
+      routeId, mediaController) {
+    this.handlers_.onBeforeInvokeHandler();
+    this.route_controller_ = this.handlers_.getMediaRouteController(routeId);
+    if (this.route_controller_) {
+      this.controller_binding_ = new bindings.Binding(
+          mediaControllerMojom.MediaController,
+          this.route_controller_, mediaController);
+      return Promise.resolve({success: true});
+    }
+    Promise.resolve({success: false});
+  };
+
   mediaRouter = new MediaRouter(new mediaRouterMojom.MediaRouterPtr(
       frameInterfaces.getInterface(mediaRouterMojom.MediaRouter.name)));
 
   return mediaRouter;
 });