Update existing uses of /wd4267 to use the GN config

extensions/utility/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/extensions.gni")
 
 assert(enable_extensions)
 
 # GYP version: extensions/extensions.gyp:extensions_utility
 source_set("utility") {
   sources = rebase_path(extensions_gypi_values.extensions_utility_sources,
                         ".",
                         "//extensions")
 
+  # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
+  configs += [ "//build/config/compiler:no_size_t_to_int_warning" ]
+
   deps = [
     "//content/public/utility",
     "//extensions/common",
     "//skia",
   ]
-
-  if (is_win) {
-    cflags = [ "/wd4267" ]  # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
-  }
 }