Clean up HID backend and API.

device/hid/hid_service_unittest.cc

-// Copyright (c) 2014 The Chromium Authors. All rights reserved.
+// 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 <string>
 #include <vector>
 
-#include "base/bind.h"
-#include "base/memory/scoped_ptr.h"
 #include "base/message_loop/message_loop.h"
-#include "device/hid/hid_connection.h"
 #include "device/hid/hid_service.h"
-#include "net/base/io_buffer.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace device {
 
 TEST(HidServiceTest, Create) {
   base::MessageLoopForIO message_loop;
   HidService* service = HidService::GetInstance();
   ASSERT_TRUE(service);
 
   std::vector<HidDeviceInfo> devices;
   service->GetDevices(&devices);
-
   for (std::vector<HidDeviceInfo>::iterator it = devices.begin();
       it != devices.end();
       ++it) {
-    ASSERT_TRUE(!it->device_id.empty());
+    ASSERT_TRUE(it->device_id != kInvalidHidDeviceId);
   }
 }
 
 }  // namespace device