Use FileDescriptorWatcher in DeviceMonitorLinux

device/hid/input_service_linux_unittest.cc

 // 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 <stddef.h>
 
 #include <vector>
 
+#include "base/files/file_descriptor_watcher_posix.h"
 #include "base/message_loop/message_loop.h"
+#include "base/run_loop.h"
 #include "device/hid/input_service_linux.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace device {
 
 TEST(InputServiceLinux, Simple) {
   base::MessageLoopForIO message_loop;
+  base::FileDescriptorWatcher file_descriptor_watcher(&message_loop);
+
   InputServiceLinux* service = InputServiceLinux::GetInstance();
 
+  // Allow the FileDescriptorWatcher in DeviceMonitorLinux to start watching.
+  base::RunLoop().RunUntilIdle();
+
   ASSERT_TRUE(service);
   std::vector<InputServiceLinux::InputDeviceInfo> devices;
   service->GetDevices(&devices);
   for (size_t i = 0; i < devices.size(); ++i)
     ASSERT_TRUE(!devices[i].id.empty());
 }
 
 }  // namespace device