Standardize usage of virtual/override/final in content/browser/

content/browser/theme_helper_mac.h

Index: content/browser/theme_helper_mac.h
diff --git a/content/browser/theme_helper_mac.h b/content/browser/theme_helper_mac.h
index 3b0e1445f26062ce109d2ed4d719317e810630e7..935ab3fe238bd09af9adc722490fba0c751800ab 100644
--- a/content/browser/theme_helper_mac.h
+++ b/content/browser/theme_helper_mac.h
@@ -33,12 +33,12 @@ class ThemeHelperMac : public NotificationObserver {
   friend struct DefaultSingletonTraits<ThemeHelperMac>;
 
   ThemeHelperMac();
-  virtual ~ThemeHelperMac();
+  ~ThemeHelperMac() override;
 
   // Overridden from NotificationObserver:
-  virtual void Observe(int type,
-                       const NotificationSource& source,
-                       const NotificationDetails& details) override;
+  void Observe(int type,
+               const NotificationSource& source,
+               const NotificationDetails& details) override;
 
   NotificationRegistrar registrar_;