Extract //device/usb mocks so that they can be shared.

device/usb/mock_usb_device_handle.cc

+// Copyright 2015 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 "device/usb/mock_usb_device_handle.h"
+
+#include "device/usb/usb_device.h"
+
+namespace device {
+
+MockUsbDeviceHandle::MockUsbDeviceHandle(UsbDevice* device) : device_(device) {
+}
+
+scoped_refptr<UsbDevice> MockUsbDeviceHandle::GetDevice() const {
+  return device_;
+}
+
+MockUsbDeviceHandle::~MockUsbDeviceHandle() {
+}
+
+}  // namespace device