[Media Router] Conditionally enable mDNS on Windows.

chrome/browser/media/router/media_router.mojom

 // 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.
 
 module media_router.interfaces;
 
 // Represents an output sink to which media can be routed.
 struct MediaSink {
   enum IconType {
     CAST,
@@ skipping 263 matching lines @@
 
   // Called when there are no more listeners for messages for |route_id|.
   // Calling this will resolve the pending |ListenForRouteMessages| callback
   // with an empty list.
   StopListeningForRouteMessages(string route_id);
 
   // Indicates that a PresentationConnection that was connected to route
   // |route_id| has been closed (via .close(), garbage collection or
   // navigation).
   DetachRoute(string route_id);
+
+  // Enables mDNS discovery. No-op if mDNS discovery is already enabled.
+  // Calling this will trigger a firewall prompt on Windows if there is not
+  // already a firewall rule for mDNS.
+  EnableMdnsDiscovery();
 };
 
 // Interface for a service which observes state changes across media
 // sources, sinks, and issues.
 interface MediaRouter {
 
   // Represents overall media sink availability states.
   // UNAVAILABLE - No sinks are available.
   // PER_SOURCE - Sinks are available, but are only compatible with specific
   //              media sources.
@@ skipping 47 matching lines @@
   // changed to |state|.
   OnPresentationConnectionStateChanged(
       string route_id, PresentationConnectionState state);
 
   // Called when the presentation connected to route |route_id| has closed.
   OnPresentationConnectionClosed(
       string route_id, PresentationConnectionCloseReason reason,
       string message);
 };