Standardize usage of virtual/override/final in base/

base/supports_user_data_unittest.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/supports_user_data.h"
 
 #include <vector>
 
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace base {
 namespace {
 
 struct TestSupportsUserData : public SupportsUserData {};
 
 struct UsesItself : public SupportsUserData::Data {
   UsesItself(SupportsUserData* supports_user_data, const void* key)
       : supports_user_data_(supports_user_data),
         key_(key) {
   }
 
-  virtual ~UsesItself() {
+  ~UsesItself() override {
     EXPECT_EQ(NULL, supports_user_data_->GetUserData(key_));
   }
 
   SupportsUserData* supports_user_data_;
   const void* key_;
 };
 
 TEST(SupportsUserDataTest, ClearWorksRecursively) {
   TestSupportsUserData supports_user_data;
   char key = 0;
   supports_user_data.SetUserData(&key,
                                  new UsesItself(&supports_user_data, &key));
   // Destruction of supports_user_data runs the actual test.
 }
 
 }  // namespace
 }  // namespace base