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

extensions/shell/browser/shell_device_client.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 "extensions/shell/browser/shell_device_client.h"
 
 #include "base/logging.h"
 #include "content/public/browser/browser_thread.h"
 #include "device/hid/hid_service.h"
 #include "device/usb/usb_service.h"
 
+using content::BrowserThread;
+
 namespace extensions {
 
 ShellDeviceClient::ShellDeviceClient() {}
 
 ShellDeviceClient::~ShellDeviceClient() {}
 
 device::UsbService* ShellDeviceClient::GetUsbService() {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
   return device::UsbService::GetInstance(
-      content::BrowserThread::GetMessageLoopProxyForThread(
-          content::BrowserThread::UI));
+      BrowserThread::GetMessageLoopProxyForThread(BrowserThread::FILE));
 }
 
 device::HidService* ShellDeviceClient::GetHidService() {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
   return device::HidService::GetInstance(
-      content::BrowserThread::GetMessageLoopProxyForThread(
-          content::BrowserThread::FILE));
+      BrowserThread::GetMessageLoopProxyForThread(BrowserThread::FILE));
 }
 
 }