Standardize usage of virtual/override/final in base/

base/threading/sequenced_worker_pool.h

Index: base/threading/sequenced_worker_pool.h
diff --git a/base/threading/sequenced_worker_pool.h b/base/threading/sequenced_worker_pool.h
index 4b1c74993d0384ad18ae95e79d0f0fd1dcda1094..63c6204ebbb79bb80bd96fe79b31554b2b767ef8 100644
--- a/base/threading/sequenced_worker_pool.h
+++ b/base/threading/sequenced_worker_pool.h
@@ -290,10 +290,10 @@ class BASE_EXPORT SequencedWorkerPool : public TaskRunner {
       WorkerShutdown shutdown_behavior);
 
   // TaskRunner implementation. Forwards to PostDelayedWorkerTask().
-  virtual bool PostDelayedTask(const tracked_objects::Location& from_here,
-                               const Closure& task,
-                               TimeDelta delay) override;
-  virtual bool RunsTasksOnCurrentThread() const override;
+  bool PostDelayedTask(const tracked_objects::Location& from_here,
+                       const Closure& task,
+                       TimeDelta delay) override;
+  bool RunsTasksOnCurrentThread() const override;
 
   // Returns true if the current thread is processing a task with the given
   // sequence_token.
@@ -336,9 +336,9 @@ class BASE_EXPORT SequencedWorkerPool : public TaskRunner {
   bool IsShutdownInProgress();
 
  protected:
-  virtual ~SequencedWorkerPool();
+  ~SequencedWorkerPool() override;
 
-  virtual void OnDestruct() const override;
+  void OnDestruct() const override;
 
  private:
   friend class RefCountedThreadSafe<SequencedWorkerPool>;