Standardize usage of virtual/override/final in extensions/

extensions/common/permissions/usb_device_permission.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_COMMON_PERMISSIONS_USB_DEVICE_PERMISSION_H_
 #define EXTENSIONS_COMMON_PERMISSIONS_USB_DEVICE_PERMISSION_H_
 
 #include "base/basictypes.h"
 #include "extensions/common/permissions/api_permission.h"
 #include "extensions/common/permissions/set_disjunction_permission.h"
 #include "extensions/common/permissions/usb_device_permission_data.h"
 
 namespace extensions {
 
 class UsbDevicePermission
   : public SetDisjunctionPermission<UsbDevicePermissionData,
                                     UsbDevicePermission> {
  public:
   struct CheckParam : public APIPermission::CheckParam {
     CheckParam(uint16 vendor_id, uint16 product_id, int interface_id)
       : vendor_id(vendor_id),
         product_id(product_id),
         interface_id(interface_id) {}
     const uint16 vendor_id;
     const uint16 product_id;
     const int interface_id;
   };
 
   explicit UsbDevicePermission(const APIPermissionInfo* info);
-  virtual ~UsbDevicePermission();
+  ~UsbDevicePermission() override;
 
   // APIPermission overrides
-  virtual PermissionMessages GetMessages() const override;
+  PermissionMessages GetMessages() const override;
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_COMMON_PERMISSIONS_USB_DEVICE_PERMISSION_H_