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

chrome/installer/util/callback_work_item.h

 // 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.
 
 #ifndef CHROME_INSTALLER_UTIL_CALLBACK_WORK_ITEM_H_
 #define CHROME_INSTALLER_UTIL_CALLBACK_WORK_ITEM_H_
 
 #include "base/callback.h"
 #include "base/compiler_specific.h"
 #include "base/gtest_prod_util.h"
@@ skipping 15 matching lines @@
 //   return true;
 // }
 //
 // void SomeFunctionThatAddsItemsToAList(WorkItemList* item_list) {
 //   ...
 //   item_list->AddCallbackWorkItem(base::Bind(&SomeWorkItemCallback));
 //   ...
 // }
 class CallbackWorkItem : public WorkItem {
  public:
-  virtual ~CallbackWorkItem();
+  ~CallbackWorkItem() override;
 
-  virtual bool Do() override;
-  virtual void Rollback() override;
+  bool Do() override;
+  void Rollback() override;
 
   bool IsRollback() const;
 
  private:
   friend class WorkItem;
 
   enum RollState {
     RS_UNDEFINED,
     RS_FORWARD,
     RS_BACKWARD,
   };
 
   CallbackWorkItem(base::Callback<bool(const CallbackWorkItem&)> callback);
 
   base::Callback<bool(const CallbackWorkItem&)> callback_;
   RollState roll_state_;
 
   FRIEND_TEST_ALL_PREFIXES(CallbackWorkItemTest, TestFailure);
   FRIEND_TEST_ALL_PREFIXES(CallbackWorkItemTest, TestForwardBackward);
 };
 
 #endif  // CHROME_INSTALLER_UTIL_CALLBACK_WORK_ITEM_H_