Standardize usage of virtual/override/final in base/

base/timer/hi_res_timer_manager.h

Index: base/timer/hi_res_timer_manager.h
diff --git a/base/timer/hi_res_timer_manager.h b/base/timer/hi_res_timer_manager.h
index bfe1f4dfc785237092b797013c999c43719f5b63..ed0e1e04ad30db05327ff83c8c46e864c064a17e 100644
--- a/base/timer/hi_res_timer_manager.h
+++ b/base/timer/hi_res_timer_manager.h
@@ -16,10 +16,10 @@ namespace base {
 class BASE_EXPORT HighResolutionTimerManager : public base::PowerObserver {
  public:
   HighResolutionTimerManager();
-  virtual ~HighResolutionTimerManager();
+  ~HighResolutionTimerManager() override;
 
   // base::PowerObserver method.
-  virtual void OnPowerStateChange(bool on_battery_power) override;
+  void OnPowerStateChange(bool on_battery_power) override;
 
   // Returns true if the hi resolution clock could be used right now.
   bool hi_res_clock_available() const { return hi_res_clock_available_; }