Standardize usage of virtual/override/final in extensions/

extensions/browser/api/dns/dns_api.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 EXTENSIONS_BROWSER_API_DNS_DNS_API_H_
 #define EXTENSIONS_BROWSER_API_DNS_DNS_API_H_
 
 #include <string>
 
 #include "extensions/browser/extension_function.h"
 #include "net/base/address_list.h"
 #include "net/base/completion_callback.h"
 #include "net/dns/host_resolver.h"
 
 namespace content {
 class ResourceContext;
 }
 
 namespace extensions {
 
 class DnsResolveFunction : public AsyncExtensionFunction {
  public:
   DECLARE_EXTENSION_FUNCTION("dns.resolve", DNS_RESOLVE)
 
   DnsResolveFunction();
 
  protected:
-  virtual ~DnsResolveFunction();
+  ~DnsResolveFunction() override;
 
   // ExtensionFunction:
-  virtual bool RunAsync() override;
+  bool RunAsync() override;
 
   void WorkOnIOThread();
   void RespondOnUIThread();
 
  private:
   void OnLookupFinished(int result);
 
   std::string hostname_;
 
   // Not owned.
   content::ResourceContext* resource_context_;
 
   bool response_;  // The value sent in SendResponse().
 
   scoped_ptr<net::HostResolver::RequestHandle> request_handle_;
   scoped_ptr<net::AddressList> addresses_;
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_BROWSER_API_DNS_DNS_API_H_