Only enable Hotwords when extensions are enabled.

chrome/chrome_browser.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.
 
 {
   'variables': {
     # All .cc, .h, .m, and .mm files under browser except for:
     # * tests and mocks.
     # * code below browser/chromeos
     # * code below browser/extensions
@@ skipping 1093 matching lines @@
       'browser/renderer_host/web_cache_manager.cc',
       'browser/renderer_host/web_cache_manager.h',
       'browser/renderer_preferences_util.cc',
       'browser/renderer_preferences_util.h',
       'browser/resources_util.cc',
       'browser/resources_util.h',
       'browser/safe_browsing/safe_browsing_tab_observer.cc',
       'browser/safe_browsing/safe_browsing_tab_observer.h',
       'browser/search/contextual_search_promo_source.cc',
       'browser/search/contextual_search_promo_source.h',
-      'browser/search/hotword_client.h',
-      'browser/search/hotword_service.cc',
-      'browser/search/hotword_service.h',
-      'browser/search/hotword_service_factory.cc',
-      'browser/search/hotword_service_factory.h',
       'browser/search/iframe_source.cc',
       'browser/search/iframe_source.h',
       'browser/search/instant_io_context.cc',
       'browser/search/instant_io_context.h',
       'browser/search/instant_service.cc',
       'browser/search/instant_service.h',
       'browser/search/instant_service_factory.cc',
       'browser/search/instant_service_factory.h',
       'browser/search/instant_service_observer.cc',
       'browser/search/instant_service_observer.h',
@@ skipping 395 matching lines @@
       'browser/guest_view/web_view/web_view_permission_helper.cc',
       'browser/guest_view/web_view/web_view_permission_helper.h',
       'browser/guest_view/web_view/web_view_renderer_state.cc',
       'browser/guest_view/web_view/web_view_renderer_state.h',
       'browser/infobars/infobar_extension_api.cc',
       'browser/infobars/infobar_extension_api.h',
       'browser/renderer_host/chrome_extension_message_filter.cc',
       'browser/renderer_host/chrome_extension_message_filter.h',
       'browser/safe_json_parser.cc',
       'browser/safe_json_parser.h',
+      'browser/search/hotword_client.h',
+      'browser/search/hotword_service.cc',
+      'browser/search/hotword_service.h',
+      'browser/search/hotword_service_factory.cc',
+      'browser/search/hotword_service_factory.h',
       'browser/speech/extension_api/tts_engine_extension_api.cc',
       'browser/speech/extension_api/tts_engine_extension_api.h',
       'browser/speech/extension_api/tts_engine_extension_observer.cc',
       'browser/speech/extension_api/tts_engine_extension_observer.h',
       'browser/speech/extension_api/tts_extension_api.cc',
       'browser/speech/extension_api/tts_extension_api.h',
       'browser/sync_file_system/conflict_resolution_policy.h',
       'browser/sync_file_system/conflict_resolution_resolver.cc',
       'browser/sync_file_system/conflict_resolution_resolver.h',
       'browser/sync_file_system/drive_backend/callback_helper.h',
@@ skipping 2042 matching lines @@
             'package_name': 'org/chromium/chrome/browser',
             'template_deps': ['browser/android/tab_load_status.h'],
           },
           'includes': [ '../build/android/java_cpp_template.gypi' ],
         },
       ],
      },
     ],
   ],
 }