Standardize usage of virtual/override/final in extensions/

extensions/browser/warning_service.h

Index: extensions/browser/warning_service.h
diff --git a/extensions/browser/warning_service.h b/extensions/browser/warning_service.h
index db7da6df57644a3ec27e22273ac4a84b08a7e652..283bf6d069dec3ceba3cb2021f9fc286c709d82e 100644
--- a/extensions/browser/warning_service.h
+++ b/extensions/browser/warning_service.h
@@ -42,7 +42,7 @@ class WarningService : public ExtensionRegistryObserver,
   // |browser_context| may be NULL for testing. In this case, be sure to not
   // insert any warnings.
   explicit WarningService(content::BrowserContext* browser_context);
-  virtual ~WarningService();
+  ~WarningService() override;
 
   // Clears all warnings of types contained in |types| and notifies observers
   // of the changed warnings.
@@ -72,10 +72,9 @@ class WarningService : public ExtensionRegistryObserver,
   void NotifyWarningsChanged();
 
   // ExtensionRegistryObserver implementation.
-  virtual void OnExtensionUnloaded(content::BrowserContext* browser_context,
-                                   const Extension* extension,
-                                   UnloadedExtensionInfo::Reason reason)
-      override;
+  void OnExtensionUnloaded(content::BrowserContext* browser_context,
+                           const Extension* extension,
+                           UnloadedExtensionInfo::Reason reason) override;
 
   // Currently existing warnings.
   WarningSet warnings_;