Standardize usage of virtual/override/final in extensions/

extensions/browser/api/usb/usb_device_resource.h

Index: extensions/browser/api/usb/usb_device_resource.h
diff --git a/extensions/browser/api/usb/usb_device_resource.h b/extensions/browser/api/usb/usb_device_resource.h
index 1d5ce603da59cbb9edb77d457bc12c72895fbe40..a0de7f356b8e28b9d48c41b13091a9f6cb75da5b 100644
--- a/extensions/browser/api/usb/usb_device_resource.h
+++ b/extensions/browser/api/usb/usb_device_resource.h
@@ -29,11 +29,11 @@ class UsbDeviceResource : public ApiResource {
 
   UsbDeviceResource(const std::string& owner_extension_id,
                     scoped_refptr<device::UsbDeviceHandle> device);
-  virtual ~UsbDeviceResource();
+  ~UsbDeviceResource() override;
 
   scoped_refptr<device::UsbDeviceHandle> device() { return device_; }
 
-  virtual bool IsPersistent() const override;
+  bool IsPersistent() const override;
 
  private:
   friend class ApiResourceManager<UsbDeviceResource>;