Add a variable use_system_xcode to GN.

components/policy/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/chrome_build.gni")
 import("//build/config/features.gni")
+import("//build/toolchain/toolchain.gni")
 import("//components/policy/resources/policy_templates.gni")
 import("//third_party/protobuf/proto_library.gni")
 import("//tools/grit/grit_rule.gni")
 
 if (is_mac) {
   import("//build/util/branding.gni")
 }
 
 if (is_component_build) {
   # External code should depend on either //components/policy/core/browser or
@@ skipping 196 matching lines @@
       sources = [
         "$policy_templates_base_dir/mac/app-Manifest.plist",
       ]
       inputs = [
         script,
       ]
       outputs = [
         "$target_gen_dir/$chrome_mac_bundle_id.manifest",
       ]
 
-      args = [
-               "plutil",
-               "-convert",
-               "xml1",
-             ] + rebase_path(sources, root_out_dir) + [ "-o" ] +
-             rebase_path(outputs, root_out_dir)
+      if (use_system_xcode) {
+        args = []
+      } else {
+        args = [
+          "--developer_dir",
+          hermetic_xcode_path,
+        ]
+      }
+      args += [
+                "plutil",
+                "-convert",
+                "xml1",
+              ] + rebase_path(sources, root_out_dir) + [ "-o" ] +
+              rebase_path(outputs, root_out_dir)
 
       deps = [
         ":policy_templates",
       ]
     }
 
     bundle_data("manifest_bundle_data") {
       sources = get_target_outputs(":convert_mcx_plist")
       outputs = [
         "{{bundle_resources_dir}}/{{source_file_part}}",
@@ skipping 68 matching lines @@
                "--grit_info",
                rebase_path(grit_info_script, root_build_dir),
              ] + grit_defines
       deps = [
         ":add_version",
         ":policy_templates",
       ]
     }
   }
 }