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 99778a1d5963f6ac8d85f628e4b30b56c1ac422e..28975cf4cf9281ee395c6c9dbc7feaeff7d682a1 100644
--- a/chrome/browser/extensions/extension_service.cc
+++ b/chrome/browser/extensions/extension_service.cc
@@ -2590,17 +2590,6 @@ void ExtensionService::Observe(int type,
                      process->GetID()));
       break;
     }
-    case chrome::NOTIFICATION_PREF_CHANGED: {
-      std::string* pref_name = content::Details<std::string>(details).ptr();
-      if (*pref_name == prefs::kExtensionInstallAllowList ||
-          *pref_name == prefs::kExtensionInstallDenyList) {
-        IdentifyAlertableExtensions();
-        CheckManagementPolicy();
-      } else {
-        NOTREACHED() << "Unexpected preference name.";
-      }
-      break;
-    }
     case chrome::NOTIFICATION_IMPORT_FINISHED: {
       InitAfterImport();
       break;
@@ -2611,6 +2600,17 @@ void ExtensionService::Observe(int type,
   }
 }
 
+void ExtensionService::OnPreferenceChanged(PrefServiceBase* service,
+                                           const std::string& pref_name) {
+  if (pref_name == prefs::kExtensionInstallAllowList ||
+      pref_name == prefs::kExtensionInstallDenyList) {
+    IdentifyAlertableExtensions();
+    CheckManagementPolicy();
+  } else {
+    NOTREACHED() << "Unexpected preference name.";
+  }
+}
+
 bool ExtensionService::HasApps() const {
   return !GetAppIds().empty();
 }