Manage UsbService lifetime in DeviceClient implementations.

device/usb/usb_context.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 "device/usb/usb_context.h"
 
 #include "base/atomicops.h"
 #include "base/logging.h"
 #include "base/threading/simple_thread.h"
 #include "device/usb/usb_error.h"
@@ skipping 49 matching lines @@
   libusb_interrupt_handle_event(context_);
 }
 
 UsbContext::UsbContext(PlatformUsbContext context) : context_(context) {
   // Ownership of the PlatformUsbContext is passed to the event handler thread.
   event_handler_.reset(new UsbEventHandler(context_));
   event_handler_->Start();
 }
 
 UsbContext::~UsbContext() {
-  DCHECK(thread_checker_.CalledOnValidThread());
   event_handler_->Stop();
   event_handler_->Join();
 }
 
 }  // namespace device