Standardize usage of virtual/override/final in base/

base/memory/linked_ptr_unittest.cc

Index: base/memory/linked_ptr_unittest.cc
diff --git a/base/memory/linked_ptr_unittest.cc b/base/memory/linked_ptr_unittest.cc
index 2dbc4bdd8a21a40384bcf60368b392e10313c851..f6bc410942b95308a9572367f7a8351d9f1b1447 100644
--- a/base/memory/linked_ptr_unittest.cc
+++ b/base/memory/linked_ptr_unittest.cc
@@ -25,10 +25,8 @@ struct A {
 // Subclass
 struct B: public A {
   B() { history += base::StringPrintf("B%d ctor\n", mynum); }
-  virtual ~B() { history += base::StringPrintf("B%d dtor\n", mynum); }
-  virtual void Use() override {
-    history += base::StringPrintf("B%d use\n", mynum);
-  }
+  ~B() override { history += base::StringPrintf("B%d dtor\n", mynum); }
+  void Use() override { history += base::StringPrintf("B%d use\n", mynum); }
 };
 
 }  // namespace