Introduce the NotificationIdGenerator in //content.

content/content_tests.gypi

 # Copyright (c) 2013 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': {
     'layouttest_support_content_sources': [
       'public/test/layouttest_support.h',
       'public/test/nested_message_pump_android.cc',
       'public/test/nested_message_pump_android.h',
@@ skipping 466 matching lines @@
       'browser/media/capture/video_capture_oracle_unittest.cc',
       'browser/media/capture/web_contents_audio_input_stream_unittest.cc',
       'browser/media/capture/web_contents_video_capture_device_unittest.cc',
       'browser/media/media_internals_unittest.cc',
       'browser/media/midi_host_unittest.cc',
       'browser/media/webrtc_identity_store_unittest.cc',
       'browser/net/quota_policy_cookie_store_unittest.cc',
       'browser/notification_service_impl_unittest.cc',
       'browser/notifications/notification_database_data_unittest.cc',
       'browser/notifications/notification_database_unittest.cc',
+      'browser/notifications/notification_id_generator_unittest.cc',
       'browser/notifications/platform_notification_context_unittest.cc',
       'browser/power_monitor_message_broadcaster_unittest.cc',
       'browser/power_profiler/power_profiler_service_unittest.cc',
       'browser/power_usage_monitor_impl_unittest.cc',
       'browser/presentation/presentation_service_impl_unittest.cc',
       'browser/presentation/presentation_type_converters_unittest.cc',
       'browser/quota/mock_quota_manager.cc',
       'browser/quota/mock_quota_manager.h',
       'browser/quota/mock_quota_manager_proxy.cc',
       'browser/quota/mock_quota_manager_proxy.h',
@@ skipping 1654 matching lines @@
                   'files': ['<(PRODUCT_DIR)/libnpapi_test_plugin.so'],
                 },
               ],
             }],
           ],
         },
       ],
     }],
   ],
 }