Enable use_once_callback on mojom GN rule by default

ui/message_center/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("mojo") {
   sources = [
     "notification.mojom",
   ]
 
   public_deps = [
     "//mojo/common:common_custom_types",
     "//skia/public/interfaces:interfaces",
     "//url/mojo:url_mojom_gurl",
   ]
 }
 
 mojom("test_interfaces") {
   testonly = true
   sources = [
     "traits_test_service.mojom",
   ]
 
   public_deps = [
     ":mojo",
   ]
+
+  # TODO(crbug.com/714018): Convert the implementation to use OnceCallback.
+  use_once_callback = false
 }
 
 source_set("struct_traits") {
   sources = [
     "notification_struct_traits.cc",
     "notification_struct_traits.h",
   ]
 
   public_deps = [
     ":mojo_shared_cpp_sources",
     "//base",
     "//mojo/common:struct_traits",
     "//mojo/public/cpp/bindings",
     "//skia/public/interfaces",
     "//ui/gfx",
     "//ui/message_center",
     "//url/mojo:url_mojom_gurl",
   ]
 }