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

extensions/browser/api/usb/usb_apitest.cc

Index: extensions/browser/api/usb/usb_apitest.cc
diff --git a/extensions/browser/api/usb/usb_apitest.cc b/extensions/browser/api/usb/usb_apitest.cc
index affc107661860f74a50edb64385d9bb5ae4edbb8..a1bdc83d8cb331ed55c63f3d4f59738fd7efdd9d 100644
--- a/extensions/browser/api/usb/usb_apitest.cc
+++ b/extensions/browser/api/usb/usb_apitest.cc
@@ -130,9 +130,7 @@ class MockUsbDeviceHandle : public UsbDeviceHandle {
                     int alternate_setting,
                     const ResultCallback& callback));
 
-  virtual scoped_refptr<UsbDevice> GetDevice() const override {
-    return device_;
-  }
+  scoped_refptr<UsbDevice> GetDevice() const override { return device_; }
 
   void set_device(UsbDevice* device) { device_ = device; }