[MediaRouter] Update MR-2-Extension's PostMessage to return boolean.

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 {
   // The sink identifier, e.g. "rs71w7mFzYLFlabir_qO4NHl6SUc."
   string sink_id;
@@ skipping 78 matching lines @@
   // If the operation failed, |route| will be null and |error_text|
   //     will be set.
   CreateRoute(string media_source, string sink_id) =>
       (MediaRoute? route, string? error_text);
 
   // Closes the route specified by |route_id|.
   CloseRoute(string route_id);
 
   // Sends |message| with optional |extra_info_json| via the media route
   // |media_route_id|.
-  PostMessage(string media_route_id, string message);
+  // If the operation was sucessfull, |sent| is true; otherwise it is false.
+  PostMessage(string media_route_id, string message) => (bool sent);
 
   // Starts querying for sinks capable of displaying |media_source|.
   StartObservingMediaSinks(string media_source);
 
   // Stops querying sinks for |media_source|.
   StopObservingMediaSinks(string media_source);
 
   // Starts reporting the state of active media routes via
   // OnRoutesUpdated(). Querying will continue until
   // StopObservingMediaRoutes() is called.
@@ skipping 22 matching lines @@
   // Called when the Media Route Manager receives a route message.
   OnMessage(string media_source, string message);
 
   // Called when issues are reported for media routes.
   OnIssue(Issue issue);
 
   // Called when list of routes has been updated.
   OnRoutesUpdated(array<MediaRoute> routes);
 };