Use constexpr TaskTraits constructor in net.

net/proxy/polling_proxy_config_service.cc

Index: net/proxy/polling_proxy_config_service.cc
diff --git a/net/proxy/polling_proxy_config_service.cc b/net/proxy/polling_proxy_config_service.cc
index af6fc9cb630988cc126c6964e1be0c49f12a6360..500340e7bdf6d428084b95c051365ac722b77b10 100644
--- a/net/proxy/polling_proxy_config_service.cc
+++ b/net/proxy/polling_proxy_config_service.cc
@@ -91,8 +91,8 @@ class PollingProxyConfigService::Core
     poll_task_outstanding_ = true;
     poll_task_queued_ = false;
     base::PostTaskWithTraits(
-        FROM_HERE, base::TaskTraits().MayBlock().WithShutdownBehavior(
-                       base::TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN),
+        FROM_HERE,
+        {base::MayBlock(), base::TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN},
         base::Bind(&Core::PollAsync, this, get_config_func_));
   }