Enable use_once_callback on mojom GN rule by default

url/mojo/BUILD.gn

 # Copyright 2016 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.
 
 import("//mojo/public/tools/bindings/mojom.gni")
 
 mojom("url_mojom_gurl") {
   sources = [
     "url.mojom",
   ]
@@ skipping 11 matching lines @@
 
 mojom("test_url_mojom_gurl") {
   sources = [
     "url_test.mojom",
   ]
 
   public_deps = [
     ":url_mojom_gurl",
     ":url_mojom_origin",
   ]
+
+  # TODO(crbug.com/714018): Convert the implementation to use OnceCallback.
+  use_once_callback = false
 }