Use the task scheduler for blocking tasks in the USB service on Linux

device/usb/usb_service.cc

 // Copyright 2015 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_service.h"
 
 #include "base/bind.h"
 #include "base/feature_list.h"
 #include "base/location.h"
 #include "base/memory/ptr_util.h"
+#include "base/task_scheduler/post_task.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "build/build_config.h"
 #include "components/device_event_log/device_event_log.h"
 #include "device/base/features.h"
 #include "device/usb/usb_device.h"
 #include "device/usb/usb_device_handle.h"
 
 #if defined(OS_ANDROID)
 #include "device/usb/usb_service_android.h"
 #elif defined(USE_UDEV)
@@ skipping 18 matching lines @@
 void UsbService::Observer::OnDeviceRemovedCleanup(
     scoped_refptr<UsbDevice> device) {
 }
 
 void UsbService::Observer::WillDestroyUsbService() {}
 
 // static
 std::unique_ptr<UsbService> UsbService::Create(
     scoped_refptr<base::SequencedTaskRunner> blocking_task_runner) {
 #if defined(OS_ANDROID)
-  return base::WrapUnique(new UsbServiceAndroid(blocking_task_runner));
+  return base::WrapUnique(new UsbServiceAndroid());
 #elif defined(USE_UDEV)
-  return base::WrapUnique(new UsbServiceLinux(blocking_task_runner));
+  return base::WrapUnique(new UsbServiceLinux());
 #elif defined(OS_WIN)
   if (base::FeatureList::IsEnabled(kNewUsbBackend))
     return base::WrapUnique(new UsbServiceWin(blocking_task_runner));
   else
     return base::WrapUnique(new UsbServiceImpl(blocking_task_runner));
 #elif defined(OS_MACOSX)
   return base::WrapUnique(new UsbServiceImpl(blocking_task_runner));
 #else
   return nullptr;
 #endif
 }
 
+// static
+scoped_refptr<base::SequencedTaskRunner>
+UsbService::CreateBlockingTaskRunner() {
+  return base::CreateSequencedTaskRunnerWithTraits(
+      base::TaskTraits()
+          .MayBlock()
+          .WithPriority(base::TaskPriority::USER_VISIBLE)
+          .WithShutdownBehavior(
+              base::TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN));
+}
+
 UsbService::~UsbService() {
 #if DCHECK_IS_ON()
   DCHECK(did_shutdown_);
 #endif
   for (const auto& map_entry : devices_)
     map_entry.second->OnDisconnect();
   for (auto& observer : observer_list_)
     observer.WillDestroyUsbService();
 }
 
@@ skipping 92 matching lines @@
   DCHECK(CalledOnValidThread());
 
   for (auto& observer : observer_list_)
     observer.OnDeviceRemoved(device);
   device->NotifyDeviceRemoved();
   for (auto& observer : observer_list_)
     observer.OnDeviceRemovedCleanup(device);
 }
 
 }  // namespace device