The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0469523c2aafcfb307f7a9190140194d169cb72c

commit 0469523c2aafcfb307f7a9190140194d169cb72c
Author: weidongg <weidongg@chromium.org>
Date: Fri Jun 09 00:01:05 2017

Migrate upgrade notifications to observer

NotificationService makes it too easy for a random piece of code to hook
into another, so this CL migrates upgrade notification to observer.

BUG= 724540 ,268984

Review-Url: https://codereview.chromium.org/2925973002
Cr-Commit-Position: refs/heads/master@{#478127}

[modify] https://crrev.com/0469523c2aafcfb307f7a9190140194d169cb72c/chrome/browser/chrome_notification_types.h
[modify] https://crrev.com/0469523c2aafcfb307f7a9190140194d169cb72c/chrome/browser/chromeos/upgrade_detector_chromeos.cc
[modify] https://crrev.com/0469523c2aafcfb307f7a9190140194d169cb72c/chrome/browser/extensions/extension_service.cc
[modify] https://crrev.com/0469523c2aafcfb307f7a9190140194d169cb72c/chrome/browser/extensions/extension_service.h
[modify] https://crrev.com/0469523c2aafcfb307f7a9190140194d169cb72c/chrome/browser/service_process/service_process_control.cc
[modify] https://crrev.com/0469523c2aafcfb307f7a9190140194d169cb72c/chrome/browser/service_process/service_process_control.h
[modify] https://crrev.com/0469523c2aafcfb307f7a9190140194d169cb72c/chrome/browser/ui/ash/system_tray_client.cc
[modify] https://crrev.com/0469523c2aafcfb307f7a9190140194d169cb72c/chrome/browser/ui/ash/system_tray_client.h
[modify] https://crrev.com/0469523c2aafcfb307f7a9190140194d169cb72c/chrome/browser/ui/ash/system_tray_client_browsertest.cc
[modify] https://crrev.com/0469523c2aafcfb307f7a9190140194d169cb72c/chrome/browser/ui/browser_commands.cc
[modify] https://crrev.com/0469523c2aafcfb307f7a9190140194d169cb72c/chrome/browser/ui/toolbar/app_menu_icon_controller.cc
[modify] https://crrev.com/0469523c2aafcfb307f7a9190140194d169cb72c/chrome/browser/ui/toolbar/app_menu_icon_controller.h
[modify] https://crrev.com/0469523c2aafcfb307f7a9190140194d169cb72c/chrome/browser/ui/toolbar/app_menu_model_unittest.cc
[modify] https://crrev.com/0469523c2aafcfb307f7a9190140194d169cb72c/chrome/browser/ui/views/toolbar/toolbar_view.cc
[modify] https://crrev.com/0469523c2aafcfb307f7a9190140194d169cb72c/chrome/browser/ui/views/toolbar/toolbar_view.h
[modify] https://crrev.com/0469523c2aafcfb307f7a9190140194d169cb72c/chrome/browser/ui/webui/help/help_handler.cc
[modify] https://crrev.com/0469523c2aafcfb307f7a9190140194d169cb72c/chrome/browser/ui/webui/help/help_handler.h
[modify] https://crrev.com/0469523c2aafcfb307f7a9190140194d169cb72c/chrome/browser/ui/webui/settings/about_handler.cc
[modify] https://crrev.com/0469523c2aafcfb307f7a9190140194d169cb72c/chrome/browser/ui/webui/settings/about_handler.h
[modify] https://crrev.com/0469523c2aafcfb307f7a9190140194d169cb72c/chrome/browser/upgrade_detector.cc
[modify] https://crrev.com/0469523c2aafcfb307f7a9190140194d169cb72c/chrome/browser/upgrade_detector.h
[modify] https://crrev.com/0469523c2aafcfb307f7a9190140194d169cb72c/chrome/browser/upgrade_detector_impl.cc
[modify] https://crrev.com/0469523c2aafcfb307f7a9190140194d169cb72c/chrome/browser/upgrade_detector_impl_unittest.cc
[modify] https://crrev.com/0469523c2aafcfb307f7a9190140194d169cb72c/chrome/browser/upgrade_observer.h