Standardize usage of virtual/override/final in extensions/

extensions/browser/api/serial/serial_event_dispatcher.h

Index: extensions/browser/api/serial/serial_event_dispatcher.h
diff --git a/extensions/browser/api/serial/serial_event_dispatcher.h b/extensions/browser/api/serial/serial_event_dispatcher.h
index d26caaaaea6599b2490c12722eccbe6c8c294cd0..288bc625ca869c2957f83ddbbe9492fab7c53984 100644
--- a/extensions/browser/api/serial/serial_event_dispatcher.h
+++ b/extensions/browser/api/serial/serial_event_dispatcher.h
@@ -25,7 +25,7 @@ namespace core_api {
 class SerialEventDispatcher : public BrowserContextKeyedAPI {
  public:
   explicit SerialEventDispatcher(content::BrowserContext* context);
-  virtual ~SerialEventDispatcher();
+  ~SerialEventDispatcher() override;
 
   // Start receiving data and firing events for a connection.
   void PollConnection(const std::string& extension_id, int connection_id);