Enable use_once_callback on mojom GN rule by default

ui/gfx/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 = [
     "accelerated_widget.mojom",
     "buffer_types.mojom",
     "color_space.mojom",
     "icc_profile.mojom",
     "selection_bound.mojom",
     "transform.mojom",
   ]
 
   public_deps = [
     "//ui/gfx/geometry/mojo",
   ]
 }
 
 mojom("test_interfaces") {
   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 = [
     "selection_bound_struct_traits.h",
     "transform_struct_traits.h",
   ]
   public_deps = [
     ":mojo_shared_cpp_sources",
     "//mojo/public/cpp/bindings",
     "//ui/gfx",
   ]
 }