Standardize usage of virtual/override/final in base/

base/metrics/field_trial_unittest.cc

Index: base/metrics/field_trial_unittest.cc
diff --git a/base/metrics/field_trial_unittest.cc b/base/metrics/field_trial_unittest.cc
index 5080d65db55b62981d7ec73d7759d693336e2a2b..905cc22ea117b11b5c41faa3137231bfc8028dd2 100644
--- a/base/metrics/field_trial_unittest.cc
+++ b/base/metrics/field_trial_unittest.cc
@@ -44,12 +44,10 @@ class TestFieldTrialObserver : public FieldTrialList::Observer {
     FieldTrialList::AddObserver(this);
   }
 
-  virtual ~TestFieldTrialObserver() {
-    FieldTrialList::RemoveObserver(this);
-  }
+  ~TestFieldTrialObserver() override { FieldTrialList::RemoveObserver(this); }
 
-  virtual void OnFieldTrialGroupFinalized(const std::string& trial,
-                                          const std::string& group) override {
+  void OnFieldTrialGroupFinalized(const std::string& trial,
+                                  const std::string& group) override {
     trial_name_ = trial;
     group_name_ = group;
   }