Standardize usage of virtual/override/final in base/

base/files/important_file_writer_unittest.cc

 // Copyright (c) 2012 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/files/important_file_writer.h"
 
 #include "base/bind.h"
 #include "base/compiler_specific.h"
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
@@ skipping 15 matching lines @@
     NOTREACHED();
   }
   return content;
 }
 
 class DataSerializer : public ImportantFileWriter::DataSerializer {
  public:
   explicit DataSerializer(const std::string& data) : data_(data) {
   }
 
-  virtual bool SerializeData(std::string* output) override {
+  bool SerializeData(std::string* output) override {
     output->assign(data_);
     return true;
   }
 
  private:
   const std::string data_;
 };
 
 class SuccessfulWriteObserver {
  public:
@@ skipping 139 matching lines @@
   MessageLoop::current()->PostDelayedTask(
       FROM_HERE,
       MessageLoop::QuitWhenIdleClosure(),
       TimeDelta::FromMilliseconds(100));
   MessageLoop::current()->Run();
   ASSERT_TRUE(PathExists(writer.path()));
   EXPECT_EQ("baz", GetFileContent(writer.path()));
 }
 
 }  // namespace base