[Media Router] Wire through a new MRPM call to update media sinks.

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 7b83e6f0db09ac207b83e17bbd1a6e60964792c8..e50027149fb375644db3ad0c0fa562a19b209e7f 100644
--- a/extensions/renderer/resources/media_router_bindings.js
+++ b/extensions/renderer/resources/media_router_bindings.js
@@ -478,6 +478,11 @@ define('media_router_bindings', [
      * @type {function()}
      */
     this.enableMdnsDiscovery = null;
+
+    /**
+     * @type {function()}
+     */
+    this.startDiscovery = null;
   };
 
   /**
@@ -527,6 +532,7 @@ define('media_router_bindings', [
       'startObservingMediaRoutes',
       'connectRouteByRouteId',
       'enableMdnsDiscovery',
+      'startDiscovery',
     ];
     requiredHandlers.forEach(function(nextHandler) {
       if (handlers[nextHandler] === undefined) {
@@ -753,6 +759,13 @@ define('media_router_bindings', [
     this.handlers_.enableMdnsDiscovery();
   };
 
+  /**
+   * Starts discovery.
+   */
+  MediaRouteProvider.prototype.startDiscovery = function() {
+    this.handlers_.startDiscovery();
+  };
+
   mediaRouter = new MediaRouter(connector.bindHandleToProxy(
       serviceProvider.connectToService(
           mediaRouterMojom.MediaRouter.name),