Standardize usage of virtual/override/final in mojo/

mojo/bindings/js/handle.h

 // Copyright 2014 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 MOJO_BINDINGS_JS_HANDLE_H_
 #define MOJO_BINDINGS_JS_HANDLE_H_
 
 #include "base/observer_list.h"
 #include "gin/converter.h"
 #include "gin/handle.h"
@@ skipping 17 matching lines @@
 
   mojo::Handle get() const { return handle_.get(); }
   mojo::Handle release() { return handle_.release(); }
   void Close();
 
   void AddCloseObserver(HandleCloseObserver* observer);
   void RemoveCloseObserver(HandleCloseObserver* observer);
 
  protected:
   HandleWrapper(MojoHandle handle);
-  virtual ~HandleWrapper();
+  ~HandleWrapper() override;
   void NotifyCloseObservers();
 
   mojo::ScopedHandle handle_;
   ObserverList<HandleCloseObserver> close_observers_;
 };
 
 }  // namespace js
 }  // namespace mojo
 
 namespace gin {
@@ skipping 31 matching lines @@
       return false;
     }
     *out = gin::Handle<mojo::js::HandleWrapper>(val, object);
     return true;
   }
 };
 
 }  // namespace gin
 
 #endif  // MOJO_BINDINGS_JS_HANDLE_H_