[Media Router] Conditionally enable mDNS on Windows.

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 cfb36f1738ce6ad3fba17389edf7e70daed5db08..094311835cd18330918eeb444bf708a31c0c6371 100644
--- a/extensions/renderer/resources/media_router_bindings.js
+++ b/extensions/renderer/resources/media_router_bindings.js
@@ -473,6 +473,11 @@ define('media_router_bindings', [
      * @type {function()}
      */
     this.connectRouteByRouteId = null;
+
+    /**
+     * @type {function()}
+     */
+    this.enableMdnsDiscovery = null;
   };
 
   /**
@@ -520,7 +525,8 @@ define('media_router_bindings', [
       'createRoute',
       'stopObservingMediaSinks',
       'startObservingMediaRoutes',
-      'connectRouteByRouteId'
+      'connectRouteByRouteId',
+      'enableMdnsDiscovery',
     ];
     requiredHandlers.forEach(function(nextHandler) {
       if (handlers[nextHandler] === undefined) {
@@ -737,6 +743,13 @@ define('media_router_bindings', [
     this.handlers_.stopObservingMediaRoutes(sourceUrn);
   };
 
+  /**
+   * Enables mDNS device discovery.
+   */
+  MediaRouteProvider.prototype.enableMdnsDiscovery = function() {
+    this.handlers_.enableMdnsDiscovery();
+  };
+
   mediaRouter = new MediaRouter(connector.bindHandleToProxy(
       serviceProvider.connectToService(
           mediaRouterMojom.MediaRouter.name),