Update {virtual,override,final} to follow C++11 style in ash.

ash/system/user/user_card_view.cc

Index: ash/system/user/user_card_view.cc
diff --git a/ash/system/user/user_card_view.cc b/ash/system/user/user_card_view.cc
index 8d734bc5459bf1905f510867edc0bdf370820dde..8cb27e5e2aec1335304ef26787b9f2106e81e953 100644
--- a/ash/system/user/user_card_view.cc
+++ b/ash/system/user/user_card_view.cc
@@ -74,13 +74,13 @@ class MediaIndicator : public views::View, public MediaCaptureObserver {
     set_id(VIEW_ID_USER_VIEW_MEDIA_INDICATOR);
   }
 
-  virtual ~MediaIndicator() {
+  ~MediaIndicator() override {
     Shell::GetInstance()->system_tray_notifier()->RemoveMediaCaptureObserver(
         this);
   }
 
   // MediaCaptureObserver:
-  virtual void OnMediaCaptureChanged() override {
+  void OnMediaCaptureChanged() override {
     Shell* shell = Shell::GetInstance();
     content::BrowserContext* context =
         shell->session_state_delegate()->GetBrowserContextByIndex(index_);