Standardize usage of virtual/override/final in base/

base/memory/weak_ptr_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/memory/weak_ptr.h"
 
 #include <string>
 
 #include "base/bind.h"
 #include "base/debug/leak_annotations.h"
@@ skipping 44 matching lines @@
   TargetWithFactory() : factory(this) {}
   WeakPtrFactory<Target> factory;
 };
 
 // Helper class to create and destroy weak pointer copies
 // and delete objects on a background thread.
 class BackgroundThread : public Thread {
  public:
   BackgroundThread() : Thread("owner_thread") {}
 
-  virtual ~BackgroundThread() {
-    Stop();
-  }
+  ~BackgroundThread() override { Stop(); }
 
   void CreateArrowFromTarget(Arrow** arrow, Target* target) {
     WaitableEvent completion(true, false);
     message_loop()->PostTask(
         FROM_HERE,
         base::Bind(&BackgroundThread::DoCreateArrowFromTarget,
                    arrow, target, &completion));
     completion.Wait();
   }
 
@@ skipping 531 matching lines @@
   background.Start();
   background.DeleteTarget(target.release());
 
   // Main thread attempts to dereference the target, violating thread binding.
   ASSERT_DEATH(arrow.target.get(), "");
 }
 
 #endif
 
 }  // namespace base