[Extensions] Short-circuit activity logging if not enabled

extensions/extensions.gypi

 # Copyright 2015 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': {
     'extensions_common_constants_sources': [
       'common/constants.cc',
       'common/constants.h',
     ],
@@ skipping 479 matching lines @@
       'browser/api/web_request/upload_data_presenter.cc',
       'browser/api/web_request/upload_data_presenter.h',
       'browser/api/web_request/web_request_api.cc',
       'browser/api/web_request/web_request_api.h',
       'browser/api/web_request/web_request_api_constants.cc',
       'browser/api/web_request/web_request_api_constants.h',
       'browser/api/web_request/web_request_api_helpers.cc',
       'browser/api/web_request/web_request_api_helpers.h',
       'browser/api/web_request/web_request_event_details.cc',
       'browser/api/web_request/web_request_event_details.h',
-      'browser/api/web_request/web_request_event_router_delegate.cc',
       'browser/api/web_request/web_request_event_router_delegate.h',
       'browser/api/web_request/web_request_permissions.cc',
       'browser/api/web_request/web_request_permissions.h',
       'browser/api/web_request/web_request_time_tracker.cc',
       'browser/api/web_request/web_request_time_tracker.h',
+      'browser/api_activity_monitor.cc',
       'browser/api_activity_monitor.h',
       'browser/app_sorting.h',
       'browser/app_window/app_delegate.h',
       'browser/app_window/app_web_contents_helper.cc',
       'browser/app_window/app_web_contents_helper.h',
       'browser/app_window/app_window.cc',
       'browser/app_window/app_window.h',
       'browser/app_window/app_window_client.cc',
       'browser/app_window/app_window_client.h',
       'browser/app_window/app_window_contents.cc',
@@ skipping 619 matching lines @@
       'test/result_catcher.h',
       'test/test_content_utility_client.cc',
       'test/test_content_utility_client.h',
       'test/test_extensions_client.cc',
       'test/test_extensions_client.h',
       'test/test_permission_message_provider.cc',
       'test/test_permission_message_provider.h',
     ],
   },
 }