Fix assertion starting cast_shell (breaking thread IO restrictions).

ui/events/ozone/device/device_manager_manual.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 "ui/events/ozone/device/device_manager_manual.h"
 
 #include "base/files/file_enumerator.h"
+#include "base/threading/thread_restrictions.h"
 #include "ui/events/ozone/device/device_event.h"
 #include "ui/events/ozone/device/device_event_observer.h"
 
 namespace ui {
 
 DeviceManagerManual::DeviceManagerManual() {}
 
 DeviceManagerManual::~DeviceManagerManual() {}
 
 void DeviceManagerManual::ScanDevices(DeviceEventObserver* observer) {
+  base::ThreadRestrictions::ScopedAllowIO allow_io;
   base::FileEnumerator file_enum(base::FilePath("/dev/input"),
                                  false,
                                  base::FileEnumerator::FILES,
                                  "event*[0-9]");
   for (base::FilePath path = file_enum.Next(); !path.empty();
        path = file_enum.Next()) {
     DeviceEvent event(DeviceEvent::INPUT, DeviceEvent::ADD, path);
     observer->OnDeviceEvent(event);
   }
 }
 
 void DeviceManagerManual::AddObserver(DeviceEventObserver* observer) {}
 
 void DeviceManagerManual::RemoveObserver(DeviceEventObserver* observer) {}
 
 }  // namespace ui