[Media Router] Adds return value to mojo MediaRouteProvider::TerminateRoute.

chrome/browser/media/router/mojo/media_router.mojom

Index: chrome/browser/media/router/mojo/media_router.mojom
diff --git a/chrome/browser/media/router/mojo/media_router.mojom b/chrome/browser/media/router/mojo/media_router.mojom
index 816527e1d1d0c9cd3d1fc8f3cc37cb230a49a85a..1e1034b60f26aae63e0f06631fde013a77d7ebfb 100644
--- a/chrome/browser/media/router/mojo/media_router.mojom
+++ b/chrome/browser/media/router/mojo/media_router.mojom
@@ -229,8 +229,12 @@ interface MediaRouteProvider {
                              string? error_text,
                              RouteRequestResultCode result_code);
 
-  // Terminates the route specified by |route_id|.
-  TerminateRoute(string route_id);
+  // Terminates the route specified by |route_id|.  If the route was terminated
+  // successfully, |result_code| is set to OK and |error_text| is null.
+  // Otherwise, |result_code| is an error code and |error_text| describes the
+  // error.
+  TerminateRoute(string route_id) =>
+      (string? error_text, RouteRequestResultCode result_code);
 
   // Sends |message| via the media route |media_route_id|.
   // If the operation was successful, |sent| is true; otherwise it is false.