Update existing uses of /wd4267 to use the GN config

tools/json_schema_compiler/test/BUILD.gn

 # Copyright 2015 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/json_schema_api.gni")
 
 json_schema_api("api") {
   visibility = [ ":*" ]
 
   sources = [
@@ skipping 18 matching lines @@
   schemas = true
   root_namespace = "test::api::%(namespace)s"
 }
 
 source_set("test") {
   testonly = true
   sources = [
     "test_util.cc",
     "test_util.h",
   ]
+
+  # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
+  configs += [ "//build/config/compiler:no_size_t_to_int_warning" ]
+
   public_deps = [
     ":api",
   ]
-
-  if (is_win) {
-    # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
-    cflags = [ "/wd4267" ]
-  }
 }