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

chrome/browser/media/router/media_router.mojom

Index: chrome/browser/media/router/media_router.mojom
diff --git a/chrome/browser/media/router/media_router.mojom b/chrome/browser/media/router/media_router.mojom
index e67b327f5571e0419906741eeae7448f81d9ac6e..bf459870019aeb34cd70e418d543f098ab551b9c 100644
--- a/chrome/browser/media/router/media_router.mojom
+++ b/chrome/browser/media/router/media_router.mojom
@@ -94,9 +94,9 @@ interface MediaRouter {
   // 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);
+  // Sends |message| via the media route |media_route_id|.
+  // If the operation was successful, |sent| is true; otherwise it is false.
+  SendRouteMessage(string media_route_id, string message) => (bool sent);
 
   // Starts querying for sinks capable of displaying |media_source|.
   StartObservingMediaSinks(string media_source);