Migrate upgrade notifications to observer

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

Index: chrome/browser/ui/webui/help/help_handler.h
diff --git a/chrome/browser/ui/webui/help/help_handler.h b/chrome/browser/ui/webui/help/help_handler.h
index 82b088bb8a06db762d4d519807ded3b7d5c13c77..84de0e1a5811d0ae3bf66c9459839b5dff6459a3 100644
--- a/chrome/browser/ui/webui/help/help_handler.h
+++ b/chrome/browser/ui/webui/help/help_handler.h
@@ -13,9 +13,8 @@
 #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)
@@ -32,7 +31,7 @@ class ListValue;
 
 // WebUI message handler for the help page.
 class HelpHandler : public content::WebUIMessageHandler,
-                    public content::NotificationObserver {
+                    public UpgradeObserver {
  public:
   HelpHandler();
   ~HelpHandler() override;
@@ -43,10 +42,8 @@ class HelpHandler : public content::WebUIMessageHandler,
   // 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();
@@ -124,12 +121,12 @@ class HelpHandler : public content::WebUIMessageHandler,
   // 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_;