Declare TaskTraits for blocking USB tasks in a constexpr

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"
@@ skipping 25 matching lines @@
 
 void UsbService::Observer::OnDeviceRemoved(scoped_refptr<UsbDevice> device) {
 }
 
 void UsbService::Observer::OnDeviceRemovedCleanup(
     scoped_refptr<UsbDevice> device) {
 }
 
 void UsbService::Observer::WillDestroyUsbService() {}
 
+// Declare storage for this constexpr.
+constexpr base::TaskTraits UsbService::kBlockingTaskTraits;
+
 // static
 std::unique_ptr<UsbService> UsbService::Create() {
 #if defined(OS_ANDROID)
   return base::WrapUnique(new UsbServiceAndroid());
 #elif defined(USE_UDEV)
   return base::WrapUnique(new UsbServiceLinux());
 #elif defined(OS_WIN)
   if (base::FeatureList::IsEnabled(kNewUsbBackend))
     return base::WrapUnique(new UsbServiceWin());
   else
     return base::WrapUnique(new UsbServiceImpl());
 #elif defined(OS_MACOSX)
   return base::WrapUnique(new UsbServiceImpl());
 #else
   return nullptr;
 #endif
 }
 
 // static
 scoped_refptr<base::SequencedTaskRunner>
 UsbService::CreateBlockingTaskRunner() {
-  return base::CreateSequencedTaskRunnerWithTraits(
-      {base::MayBlock(), base::TaskPriority::USER_VISIBLE,
-       base::TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN});
+  return base::CreateSequencedTaskRunnerWithTraits(kBlockingTaskTraits);
 }
 
 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 94 matching lines @@
   DCHECK(CalledOnValidThread());
 
   for (auto& observer : observer_list_)
     observer.OnDeviceRemoved(device);
   device->NotifyDeviceRemoved();
   for (auto& observer : observer_list_)
     observer.OnDeviceRemovedCleanup(device);
 }
 
 }  // namespace device