Update existing uses of /wd4267 to use the GN config

extensions/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("//extensions/extensions.gni")
 import("//testing/test.gni")
 import("//tools/grit/grit_rule.gni")
 import("//tools/grit/repack.gni")
 
 assert(enable_extensions)
@@ skipping 52 matching lines @@
     "//extensions/common:mojo",
     "//extensions/common/api:mojom",
   ]
 }
 
 source_set("test_support") {
   testonly = true
   sources = rebase_path(extensions_gypi_values.extensions_test_support_sources,
                         ".",
                         "//extensions")
+  # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
+  configs += [ "//build/config/compiler:no_size_t_to_int_warning" ]
 
   deps = [
     ":extensions_resources",
     "//base",
     "//base:prefs_test_support",
     "//content/public/common",
     "//content/test:test_support",
     "//extensions/browser",
     "//extensions/common",
     "//extensions/common/api",
     "//extensions/common/api:api_registration",
     "//net:test_support",
     "//testing/gmock",
     "//testing/gtest",
   ]
 
   public_deps = [
     "//content/public/browser",
     "//extensions/common/api/cast_channel:cast_channel_proto",
   ]
-
-  if (is_win) {
-    cflags = [ "/wd4267" ]  # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
-  }
 }
 
 # GYP version: //extensions/extensions.gyp:extensions_shell_and_test_pak
 repack("shell_and_test_pak") {
   sources = [
     "$root_gen_dir/blink/public/resources/blink_resources.pak",
     "$root_gen_dir/content/app/strings/content_strings_en-US.pak",
     "$root_gen_dir/content/content_resources.pak",
     "$root_gen_dir/content/shell/shell_resources.pak",
     "$root_gen_dir/extensions/extensions_browser_resources_100_percent.pak",
@@ skipping 108 matching lines @@
   ]
 
   if (is_win) {
     deps += [ "//base/allocator" ]
   }
 
   if (is_mac) {
     deps += [ "shell:app_shell" ]  # Needed for App Shell.app's Helper.
   }
 }