Standardize usage of virtual/override/final in mojo/

mojo/bindings/js/waiting_callback.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_WAITING_CALLBACK_H_
 #define MOJO_BINDINGS_JS_WAITING_CALLBACK_H_
 
 #include "gin/handle.h"
 #include "gin/runner.h"
 #include "gin/wrappable.h"
@@ skipping 19 matching lines @@
 
   // Cancels the callback. Does nothing if a callback is not pending. This is
   // implicitly invoked from the destructor but can be explicitly invoked as
   // necessary.
   void Cancel();
 
  private:
   WaitingCallback(v8::Isolate* isolate,
                   v8::Handle<v8::Function> callback,
                   gin::Handle<HandleWrapper> handle_wrapper);
-  virtual ~WaitingCallback();
+  ~WaitingCallback() override;
 
   // Callback from MojoAsyncWaiter. |closure| is the WaitingCallback.
   static void CallOnHandleReady(void* closure, MojoResult result);
 
   // Invoked from CallOnHandleReady() (CallOnHandleReady() must be static).
   void OnHandleReady(MojoResult result);
 
   // Invoked by the HandleWrapper if the handle is closed while this wait is
   // still in progress.
-  virtual void OnWillCloseHandle() override;
+  void OnWillCloseHandle() override;
 
   base::WeakPtr<gin::Runner> runner_;
   MojoAsyncWaitID wait_id_;
 
   HandleWrapper* handle_wrapper_;
 
   DISALLOW_COPY_AND_ASSIGN(WaitingCallback);
 };
 
 }  // namespace js
 }  // namespace mojo
 
 #endif  // MOJO_BINDINGS_JS_WAITING_CALLBACK_H_