Update {virtual,override,final} to follow C++11 style in printing.

printing/backend/print_backend_dummy.cc

 // Copyright (c) 2010 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.
 
 // This is dummy implementation for all configurations where there is no
 // print backend.
 #if !defined(PRINT_BACKEND_AVAILABLE)
 
 #include "printing/backend/print_backend.h"
 
@@ skipping 30 matching lines @@
   std::string GetPrinterDriverInfo(
       const std::string& printer_name) override {
     return std::string();
   }
 
   bool IsValidPrinter(const std::string& printer_name) override {
     return false;
   }
 
  private:
-  ~DummyPrintBackend() {}
+  ~DummyPrintBackend() override {}
 
   DISALLOW_COPY_AND_ASSIGN(DummyPrintBackend);
 };
 
 scoped_refptr<PrintBackend> PrintBackend::CreateInstance(
     const base::DictionaryValue* print_backend_settings) {
   return new DummyPrintBackend();
 }
 
 }  // namespace printing
 
 #endif  // PRINT_BACKEND_AVAILABLE