Standardize usage of virtual/override/final in base/

base/task_runner.cc

Index: base/task_runner.cc
diff --git a/base/task_runner.cc b/base/task_runner.cc
index f2c64f370a7e65fb8a2e3b62e53a24be5faed95e..262e1f8b09eac8d9f91b4113ddeccc27a33323ad 100644
--- a/base/task_runner.cc
+++ b/base/task_runner.cc
@@ -20,8 +20,8 @@ class PostTaskAndReplyTaskRunner : public internal::PostTaskAndReplyImpl {
   explicit PostTaskAndReplyTaskRunner(TaskRunner* destination);
 
  private:
-  virtual bool PostTask(const tracked_objects::Location& from_here,
-                        const Closure& task) override;
+  bool PostTask(const tracked_objects::Location& from_here,
+                const Closure& task) override;
 
   // Non-owning.
   TaskRunner* destination_;