Log errors from libusb.

components/usb_service/usb_error.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 COMPONENTS_USB_SERVICE_USB_ERROR_H_
+#define COMPONENTS_USB_SERVICE_USB_ERROR_H_
+
+#include <string>
+
+namespace usb_service {
+
+// A number of libusb functions which return a member of enum libusb_error
+// return an int instead so for convenience this function takes an int.
+std::string ConvertErrorToString(int errcode);
+
+}  // namespace usb_service;
+
+#endif  // COMPONENTS_USB_SERVICE_USB_ERROR_H_