Enable use_once_callback on mojom GN rule by default

extensions/common/api/BUILD.gn

 # Copyright 2014 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("//build/config/features.gni")
 import("//extensions/common/api/schema.gni")
 import("//extensions/features/features.gni")
 import("//mojo/public/tools/bindings/mojom.gni")
 import("//tools/json_schema_compiler/json_schema_api.gni")
 
@@ skipping 11 matching lines @@
   deps = [
     "//base",
     "//extensions/features",
   ]
 }
 
 mojom("mojom") {
   sources = [
     "mime_handler.mojom",
   ]
+
+  # TODO(crbug.com/714018): Convert the implementation to use OnceCallback.
+  use_once_callback = false
 }
 
 group("api") {
   public_deps = [
     ":generated_api",
     ":mojom",
     "//extensions/features",
   ]
 }