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

ash/display/display_error_observer_chromeos_unittest.cc

Index: ash/display/display_error_observer_chromeos_unittest.cc
diff --git a/ash/display/display_error_observer_chromeos_unittest.cc b/ash/display/display_error_observer_chromeos_unittest.cc
index b52afdf99696e95d05337efcd5fcfd416638fb7c..b0b3810ee41641ea0e7529a90e971e6d0d79e4e0 100644
--- a/ash/display/display_error_observer_chromeos_unittest.cc
+++ b/ash/display/display_error_observer_chromeos_unittest.cc
@@ -20,10 +20,9 @@ class DisplayErrorObserverTest : public test::AshTestBase {
   DisplayErrorObserverTest() {
   }
 
-  virtual ~DisplayErrorObserverTest() {
-  }
+  ~DisplayErrorObserverTest() override {}
 
-  virtual void SetUp() override {
+  void SetUp() override {
     test::AshTestBase::SetUp();
     observer_.reset(new DisplayErrorObserver());
   }