Use constexpr TaskTraits constructor in device.

device/usb/usb_service_impl.cc

Index: device/usb/usb_service_impl.cc
diff --git a/device/usb/usb_service_impl.cc b/device/usb/usb_service_impl.cc
index dba15d978a1564ddab092ba409003bb6a0e41f04..9881c7443bc157ec306166d51ed0aa016d7deee6 100644
--- a/device/usb/usb_service_impl.cc
+++ b/device/usb/usb_service_impl.cc
@@ -225,11 +225,8 @@ UsbServiceImpl::UsbServiceImpl()
       weak_factory_(this) {
   base::PostTaskWithTraits(
       FROM_HERE,
-      base::TaskTraits()
-          .MayBlock()
-          .WithPriority(base::TaskPriority::USER_VISIBLE)
-          .WithShutdownBehavior(
-              base::TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN),
+      {base::MayBlock(), base::TaskPriority::USER_VISIBLE,
+       base::TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN},
       base::Bind(&InitializeUsbContextOnBlockingThread, task_runner(),
                  base::Bind(&UsbServiceImpl::OnUsbContext,
                             weak_factory_.GetWeakPtr())));
@@ -329,17 +326,13 @@ void UsbServiceImpl::RefreshDevices() {
     pending_path_enumerations_.pop();
   }
 
-  base::PostTaskWithTraits(
-      FROM_HERE,
-      base::TaskTraits()
-          .MayBlock()
-          .WithPriority(base::TaskPriority::USER_VISIBLE)
-          .WithShutdownBehavior(
-              base::TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN),
-      base::Bind(&GetDeviceListOnBlockingThread, device_path, context_,
-                 task_runner(),
-                 base::Bind(&UsbServiceImpl::OnDeviceList,
-                            weak_factory_.GetWeakPtr())));
+  base::PostTaskWithTraits(FROM_HERE,
+                           {base::MayBlock(), base::TaskPriority::USER_VISIBLE,
+                            base::TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN},

[Reilly Grant (use Gerrit), 2017/05/03 20:27:00]

Since these are the same traits I use in UsbService::CreateBlockingTaskRunner
can you define these as a static constexpr there so that I can simply refer to
them here?

[fdoray, 2017/05/03 20:45:44]

This would indeed be a nice improvement but in the context of automated mass
refactoring we do not have the bandwidth for such per file changes and leave it
up to the owners to fix up local tweaks.

+                           base::Bind(&GetDeviceListOnBlockingThread,
+                                      device_path, context_, task_runner(),
+                                      base::Bind(&UsbServiceImpl::OnDeviceList,
+                                                 weak_factory_.GetWeakPtr())));
 }
 
 void UsbServiceImpl::OnDeviceList(libusb_device** platform_devices,