Only enable Hotwords when extensions are enabled.

chrome/chrome_tests_unit.gypi

 # Copyright 2012 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.
 {
   'targets': [
     {
       # This target contains mocks and test utilities that don't belong in
       # production libraries but are used by more than one test executable.
       'target_name': 'test_support_common',
       'type': 'static_library',
@@ skipping 2131 matching lines @@
             'browser/extensions/menu_manager_unittest.cc',
             'browser/extensions/pack_extension_unittest.cc',
             'browser/extensions/page_action_controller_unittest.cc',
             'browser/extensions/permissions_updater_unittest.cc',
             'browser/extensions/sandboxed_unpacker_unittest.cc',
             'browser/extensions/updater/extension_updater_unittest.cc',
             'browser/extensions/user_script_listener_unittest.cc',
             'browser/extensions/webstore_inline_installer_unittest.cc',
             'browser/extensions/webstore_installer_unittest.cc',
             'browser/guest_view/guest_view_manager_unittest.cc',
+            'browser/search/hotword_service_unittest.cc',
             'browser/web_applications/web_app_unittest.cc',
             'common/extensions/sync_type_unittest.cc',
             'common/extensions/permissions/permission_set_unittest.cc',
             'renderer/extensions/event_unittest.cc',
             'renderer/extensions/extension_localization_peer_unittest.cc',
             'renderer/extensions/json_schema_unittest.cc',
             'renderer/extensions/messaging_utils_unittest.cc',
             'renderer/extensions/module_system_unittest.cc',
             'renderer/extensions/renderer_permissions_policy_delegate_unittest.cc',
             'renderer/extensions/safe_builtins_unittest.cc',
@@ skipping 755 matching lines @@
             'unit_tests.isolate',
           ],
           'sources': [
             'unit_tests.isolate',
           ],
         },
       ],
     }],
   ],  # 'conditions'
 }