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

ash/system/chromeos/power/tray_power.cc

Index: ash/system/chromeos/power/tray_power.cc
diff --git a/ash/system/chromeos/power/tray_power.cc b/ash/system/chromeos/power/tray_power.cc
index 3692cc2e3ef22cdb08f04cf9af20df0e0b9d782e..969a1ddf75a4859e86035db897e1455603d4aeb4 100644
--- a/ash/system/chromeos/power/tray_power.cc
+++ b/ash/system/chromeos/power/tray_power.cc
@@ -47,11 +47,10 @@ class PowerTrayView : public views::ImageView {
     UpdateImage();
   }
 
-  virtual ~PowerTrayView() {
-  }
+  ~PowerTrayView() override {}
 
   // Overriden from views::View.
-  virtual void GetAccessibleState(ui::AXViewState* state) override {
+  void GetAccessibleState(ui::AXViewState* state) override {
     state->name = accessible_name_;
     state->role = ui::AX_ROLE_BUTTON;
   }