Introduce the NotificationIdGenerator in //content.

content/content_browser.gypi

 # Copyright (c) 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.
 
 {
   'dependencies': [
     '../base/base.gyp:base_static',
     '../crypto/crypto.gyp:crypto',
     '../device/battery/battery.gyp:device_battery',
     '../device/battery/battery.gyp:device_battery_mojo_bindings',
@@ skipping 1024 matching lines @@
       'browser/net/view_http_cache_job_factory.cc',
       'browser/net/view_http_cache_job_factory.h',
       'browser/notification_service_impl.cc',
       'browser/notification_service_impl.h',
       'browser/notifications/notification_database.cc',
       'browser/notifications/notification_database.h',
       'browser/notifications/notification_database_data_conversions.cc',
       'browser/notifications/notification_database_data_conversions.h',
       'browser/notifications/notification_event_dispatcher_impl.cc',
       'browser/notifications/notification_event_dispatcher_impl.h',
+      'browser/notifications/notification_id_generator.cc',
+      'browser/notifications/notification_id_generator.h',
       'browser/notifications/notification_message_filter.cc',
       'browser/notifications/notification_message_filter.h',
       'browser/notifications/page_notification_delegate.cc',
       'browser/notifications/page_notification_delegate.h',
       'browser/notifications/platform_notification_context_impl.cc',
       'browser/notifications/platform_notification_context_impl.h',
       'browser/permissions/permission_service_context.cc',
       'browser/permissions/permission_service_context.h',
       'browser/permissions/permission_service_impl.cc',
       'browser/permissions/permission_service_impl.h',
@@ skipping 991 matching lines @@
         'browser/media/media_web_contents_observer.h',
       ],
     }],
     ['OS == "linux" and use_openssl==1', {
       'dependencies': [
         '../third_party/boringssl/boringssl.gyp:boringssl',
       ],
     }],
   ],
 }