Standardize usage of virtual/override/final in extensions/

extensions/browser/extension_message_filter.h

Index: extensions/browser/extension_message_filter.h
diff --git a/extensions/browser/extension_message_filter.h b/extensions/browser/extension_message_filter.h
index ce65a499e0a144fd68509eb1b77cfa00b6dde499..7d2972a6c4b0eadd36ae518801f5a0b68e467fcc 100644
--- a/extensions/browser/extension_message_filter.h
+++ b/extensions/browser/extension_message_filter.h
@@ -43,14 +43,13 @@ class ExtensionMessageFilter : public content::BrowserMessageFilter {
   friend class content::BrowserThread;
   friend class base::DeleteHelper<ExtensionMessageFilter>;
 
-  virtual ~ExtensionMessageFilter();
+  ~ExtensionMessageFilter() override;
 
   // content::BrowserMessageFilter implementation.
-  virtual void OverrideThreadForMessage(
-      const IPC::Message& message,
-      content::BrowserThread::ID* thread) override;
-  virtual void OnDestruct() const override;
-  virtual bool OnMessageReceived(const IPC::Message& message) override;
+  void OverrideThreadForMessage(const IPC::Message& message,
+                                content::BrowserThread::ID* thread) override;
+  void OnDestruct() const override;
+  bool OnMessageReceived(const IPC::Message& message) override;
 
   // Message handlers on the UI thread.
   void OnExtensionAddListener(const std::string& extension_id,