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

extensions/renderer/resources/media_router_bindings.js

Index: extensions/renderer/resources/media_router_bindings.js
diff --git a/extensions/renderer/resources/media_router_bindings.js b/extensions/renderer/resources/media_router_bindings.js
index 7aeb83d8eb996b68e27a98ff2c8ef5a2359caae5..f0d0aca3ad7645c8b498fef7a9c933dd6c462ad6 100644
--- a/extensions/renderer/resources/media_router_bindings.js
+++ b/extensions/renderer/resources/media_router_bindings.js
@@ -6,12 +6,14 @@ 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,
@@ -842,6 +844,19 @@ define('media_router_bindings', [
     });
   };
 
+  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)));