Move enable extensions define to a build flag.

components/policy/core/common/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")
 
 group("common") {
   if (is_component_build) {
     public_deps = [
       "//components/policy",
@@ skipping 129 matching lines @@
     public_deps = [
       "//components/policy:generated",
       "//components/policy/proto",
     ]
     deps = [
       "//base:i18n",
       "//base/third_party/dynamic_annotations",
       "//components/data_use_measurement/core",
       "//components/json_schema",
       "//components/prefs",
+      "//extensions/features",
       "//google_apis",
       "//net",
       "//third_party/re2",
       "//url",
     ]
 
     if (is_win) {
       libs = [
         "shlwapi.lib",
         "userenv.lib",
@@ skipping 123 matching lines @@
       "//crypto",
       "//net",
       "//testing/gmock",
       "//testing/gtest",
     ]
   }
 
   source_set("unit_tests") {
     testonly = true
     sources = [
+      "//extensions/features",
       "cloud/cloud_policy_client_unittest.cc",
       "cloud/cloud_policy_core_unittest.cc",
       "cloud/cloud_policy_manager_unittest.cc",
       "cloud/cloud_policy_refresh_scheduler_unittest.cc",
       "cloud/cloud_policy_service_unittest.cc",
       "cloud/cloud_policy_validator_unittest.cc",
       "cloud/device_management_service_unittest.cc",
       "cloud/policy_header_io_helper_unittest.cc",
       "cloud/policy_header_service_unittest.cc",
       "cloud/user_info_fetcher_unittest.cc",
@@ skipping 46 matching lines @@
         "//chrome/test/data/policy/",
       ]
     }
 
     deps = [
       ":test_support",
       "//base",
       "//base/test:test_support",
       "//components/policy:generated",
       "//components/prefs:test_support",
+      "//extensions/features",
       "//google_apis",
       "//net:test_support",
       "//testing/gmock",
       "//testing/gtest",
     ]
   }
 }