Migrate upgrade notifications to observer

chrome/browser/ui/webui/help/help_handler.h

 // 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.
 
 #ifndef CHROME_BROWSER_UI_WEBUI_HELP_HELP_HANDLER_H_
 #define CHROME_BROWSER_UI_WEBUI_HELP_HELP_HANDLER_H_
 
 #include <string>
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "base/strings/string16.h"
 #include "build/build_config.h"
 #include "chrome/browser/ui/webui/help/version_updater.h"
+#include "chrome/browser/upgrade_observer.h"
 #include "components/policy/core/common/policy_service.h"
-#include "content/public/browser/notification_observer.h"
-#include "content/public/browser/notification_registrar.h"
 #include "content/public/browser/web_ui_message_handler.h"
 
 #if defined(OS_CHROMEOS)
 #include "base/task/cancelable_task_tracker.h"
 #include "chromeos/system/version_loader.h"
 #include "third_party/cros_system_api/dbus/update_engine/dbus-constants.h"
 #endif  // defined(OS_CHROMEOS)
 
 namespace base {
 class DictionaryValue;
 class FilePath;
 class ListValue;
 }
 
 // WebUI message handler for the help page.
 class HelpHandler : public content::WebUIMessageHandler,
-                    public content::NotificationObserver {
+                    public UpgradeObserver {
  public:
   HelpHandler();
   ~HelpHandler() override;
 
   // WebUIMessageHandler implementation.
   void RegisterMessages() override;
 
   // Adds string values for the UI to |localized_strings|.
   static void GetLocalizedValues(base::DictionaryValue* localized_strings);
 
-  // NotificationObserver implementation.
-  void Observe(int type,
-               const content::NotificationSource& source,
-               const content::NotificationDetails& details) override;
+  // UpgradeObserver implementation.
+  void OnUpgradeRecommended() override;
 
   // Returns the browser version as a string.
   static base::string16 BuildBrowserVersionString();
 
  private:
   void OnDeviceAutoUpdatePolicyChanged(const base::Value* previous_policy,
                                        const base::Value* current_policy);
 
   // On ChromeOS, this gets the current update status. On other platforms, it
   // will request and perform an update (if one is available).
@@ skipping 57 matching lines @@
   // Callback for setting the regulatory label alt text.
   void OnRegulatoryLabelTextRead(const std::string& text);
 
   // Callback for setting the eol string text.
   void OnEolStatus(update_engine::EndOfLifeStatus status);
 #endif
 
   // Specialized instance of the VersionUpdater used to update the browser.
   std::unique_ptr<VersionUpdater> version_updater_;
 
-  // Used to observe notifications.
-  content::NotificationRegistrar registrar_;
-
   // Used to observe changes in the |kDeviceAutoUpdateDisabled| policy.
   policy::PolicyChangeRegistrar policy_registrar_;
 
+  // Whether to start listening to upgrade detector.

[sky, 2017/06/08 18:09:52]

How about: If true changes to UpgradeObserver are applied, if false they are
ignored.
Same comment in the other places you use this pattern.
Maybe rename to apply_changes_from_upgrade_observer_?

[weidongg, 2017/06/08 18:58:07]

Yes, that's better, thanks. Done. 

+  bool enable_upgrade_observer_;
+
   // Used for callbacks.
   base::WeakPtrFactory<HelpHandler> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(HelpHandler);
 };
 
 #endif  // CHROME_BROWSER_UI_WEBUI_HELP_HELP_HANDLER_H_