Move device/usb classes from the FILE thread to UI thread.

extensions/browser/api/usb/usb_device_resource.h

 // 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.
 
 #ifndef EXTENSIONS_BROWSER_API_USB_USB_DEVICE_RESOURCE_H_
 #define EXTENSIONS_BROWSER_API_USB_USB_DEVICE_RESOURCE_H_
 
 #include <string>
 
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
 #include "base/synchronization/lock.h"
 #include "content/public/browser/browser_thread.h"
 #include "device/usb/usb_device_handle.h"
 #include "extensions/browser/api/api_resource.h"
 #include "extensions/browser/api/api_resource_manager.h"
 
 namespace usb_service {
 class UsbDeviceHandle;
 }
 
 namespace extensions {
 
 // A UsbDeviceResource is an ApiResource wrapper for a UsbDevice.
 class UsbDeviceResource : public ApiResource {
  public:
   static const content::BrowserThread::ID kThreadId =
-      content::BrowserThread::FILE;
+      content::BrowserThread::UI;
 
   UsbDeviceResource(const std::string& owner_extension_id,
                     scoped_refptr<device::UsbDeviceHandle> device);
   ~UsbDeviceResource() override;
 
   scoped_refptr<device::UsbDeviceHandle> device() { return device_; }
 
   bool IsPersistent() const override;
 
  private:
   friend class ApiResourceManager<UsbDeviceResource>;
   static const char* service_name() { return "UsbDeviceResourceManager"; }
 
   scoped_refptr<device::UsbDeviceHandle> device_;
 
   DISALLOW_COPY_AND_ASSIGN(UsbDeviceResource);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_BROWSER_API_USB_USB_DEVICE_RESOURCE_H_