PushMessagingNotificationManager: extract IsTabVisible and test it.

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.
 {
   'variables': {
     'chrome_unit_tests_sources': [
       # histograms.xml is analyzed by AboutFlagsHistogramTest, so this
       # dependency is needed to make commit bots run unit_tests on
       # histograms.xml changes.
       '../tools/metrics/histograms/histograms.xml',
@@ skipping 180 matching lines @@
       'browser/profiles/gaia_info_update_service_unittest.cc',
       'browser/profiles/profile_attributes_storage_unittest.cc',
       'browser/profiles/profile_avatar_icon_util_unittest.cc',
       'browser/profiles/profile_downloader_unittest.cc',
       'browser/profiles/profile_info_cache_unittest.cc',
       'browser/profiles/profile_info_cache_unittest.h',
       'browser/profiles/profile_manager_unittest.cc',
       'browser/profiles/profile_statistics_unittest.cc',
       'browser/profiles/profile_shortcut_manager_unittest_win.cc',
       'browser/push_messaging/push_messaging_app_identifier_unittest.cc',
+      'browser/push_messaging/push_messaging_notification_manager_unittest.cc',
       'browser/push_messaging/push_messaging_permission_context_unittest.cc',
       'browser/renderer_host/chrome_render_widget_host_view_mac_history_swiper_unit_test.mm',
       'browser/resources_util_unittest.cc',
       'browser/search/contextual_search_policy_handler_android_unittest.cc',
       'browser/search/iframe_source_unittest.cc',
       'browser/search/thumbnail_source_unittest.cc',
       'browser/search_engines/search_provider_install_data_unittest.cc',
       'browser/service_process/service_process_control_mac_unittest.mm',
       'browser/services/gcm/fake_gcm_profile_service.cc',
       'browser/services/gcm/fake_gcm_profile_service.h',
@@ skipping 2777 matching lines @@
               'dependencies': [
                 '../tools/xdisplaycheck/xdisplaycheck.gyp:xdisplaycheck',
               ],
             }],
           ],
         },
       ],
     }],
   ],  # 'conditions'
 }