Log errors from libusb.

components/usb_service/usb_error.cc

Index: components/usb_service/usb_error.cc
diff --git a/components/usb_service/usb_error.cc b/components/usb_service/usb_error.cc
new file mode 100644
index 0000000000000000000000000000000000000000..d3e99601205a4c1384c96d811458588739419bdc
--- /dev/null
+++ b/components/usb_service/usb_error.cc
@@ -0,0 +1,15 @@
+// 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.
+
+#include "components/usb_service/usb_error.h"
+
+#include "third_party/libusb/src/libusb/libusb.h"
+
+namespace usb_service {
+
+std::string ConvertErrorToString(int errcode) {
+  return libusb_strerror(static_cast<libusb_error>(errcode));
+}
+
+}  // namespace usb_service;