Declare TaskTraits for blocking USB tasks in a constexpr

device/usb/usb_service_impl.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_service_impl.h"
 
 #include <stdint.h>
 
 #include <list>
 #include <memory>
@@ skipping 204 matching lines @@
 
 }  // namespace
 
 UsbServiceImpl::UsbServiceImpl()
     : UsbService(nullptr),
 #if defined(OS_WIN)
       device_observer_(this),
 #endif
       weak_factory_(this) {
   base::PostTaskWithTraits(
-      FROM_HERE,
-      {base::MayBlock(), base::TaskPriority::USER_VISIBLE,
-       base::TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN},
+      FROM_HERE, kBlockingTaskTraits,
       base::Bind(&InitializeUsbContextOnBlockingThread, task_runner(),
                  base::Bind(&UsbServiceImpl::OnUsbContext,
                             weak_factory_.GetWeakPtr())));
 }
 
 UsbServiceImpl::~UsbServiceImpl() {
   if (hotplug_enabled_)
     libusb_hotplug_deregister_callback(context_->context(), hotplug_handle_);
   for (auto* platform_device : ignored_devices_)
     libusb_unref_device(platform_device);
@@ skipping 79 matching lines @@
 
   enumeration_in_progress_ = true;
   DCHECK(devices_being_enumerated_.empty());
 
   std::string device_path;
   if (!pending_path_enumerations_.empty()) {
     device_path = pending_path_enumerations_.front();
     pending_path_enumerations_.pop();
   }
 
-  base::PostTaskWithTraits(FROM_HERE,
-                           {base::MayBlock(), base::TaskPriority::USER_VISIBLE,
-                            base::TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN},
+  base::PostTaskWithTraits(FROM_HERE, kBlockingTaskTraits,
                            base::Bind(&GetDeviceListOnBlockingThread,
                                       device_path, context_, task_runner(),
                                       base::Bind(&UsbServiceImpl::OnDeviceList,
                                                  weak_factory_.GetWeakPtr())));
 }
 
 void UsbServiceImpl::OnDeviceList(libusb_device** platform_devices,
                                   size_t device_count) {
   DCHECK(CalledOnValidThread());
   if (!platform_devices) {
@@ skipping 213 matching lines @@
 }
 
 void UsbServiceImpl::EnumerationFailed(PlatformUsbDevice platform_device,
                                        const base::Closure& refresh_complete) {
   libusb_ref_device(platform_device);
   ignored_devices_.insert(platform_device);
   refresh_complete.Run();
 }
 
 }  // namespace device