Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/extensions/extension_service.cc

Index: chrome/browser/extensions/extension_service.cc
diff --git a/chrome/browser/extensions/extension_service.cc b/chrome/browser/extensions/extension_service.cc
index eb41d529dee28be3cbc8cb0e2ab7bfe6d95dc6c1..ffb8152b0fe2d9f56e6db906afb8430df754e9ca 100644
--- a/chrome/browser/extensions/extension_service.cc
+++ b/chrome/browser/extensions/extension_service.cc
@@ -2582,16 +2582,6 @@ void ExtensionService::Observe(int type,
                      process->GetID()));
       break;
     }
-    case chrome::NOTIFICATION_PREF_CHANGED: {
-      const std::string& pref_name =
-          *content::Details<std::string>(details).ptr();
-      DCHECK(pref_name == prefs::kExtensionInstallAllowList ||
-             pref_name == prefs::kExtensionInstallDenyList)
-          << "Unexpected preference name " << pref_name;
-      IdentifyAlertableExtensions();
-      CheckManagementPolicy();
-      break;
-    }
     case chrome::NOTIFICATION_IMPORT_FINISHED: {
       InitAfterImport();
       break;
@@ -2602,6 +2592,15 @@ void ExtensionService::Observe(int type,
   }
 }
 
+void ExtensionService::OnPreferenceChanged(PrefServiceBase* service,
+                                           const std::string& pref_name) {
+  DCHECK(pref_name == prefs::kExtensionInstallAllowList ||
+         pref_name == prefs::kExtensionInstallDenyList)
+      << "Unexpected preference name " << pref_name;
+  IdentifyAlertableExtensions();
+  CheckManagementPolicy();
+}
+
 bool ExtensionService::HasApps() const {
   return !GetAppIds().empty();
 }