Add constexpr TaskTraits constructor.

base/BUILD.gn

 # Copyright (c) 2013 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.
 
 # HOW TO WRITE CONDITIONALS IN THIS FILE
 # ======================================
 #
 # In many other places, one would write a conditional that expresses all the
 # cases when a source file is used or unused, and then either add or subtract
 # it from the sources list in that case
@@ skipping 2096 matching lines @@
     "task_scheduler/scheduler_single_thread_task_runner_manager_unittest.cc",
     "task_scheduler/scheduler_worker_pool_impl_unittest.cc",
     "task_scheduler/scheduler_worker_stack_unittest.cc",
     "task_scheduler/scheduler_worker_unittest.cc",
     "task_scheduler/scoped_set_task_priority_for_current_thread_unittest.cc",
     "task_scheduler/sequence_sort_key_unittest.cc",
     "task_scheduler/sequence_unittest.cc",
     "task_scheduler/task_scheduler_impl_unittest.cc",
     "task_scheduler/task_tracker_posix_unittest.cc",
     "task_scheduler/task_tracker_unittest.cc",
+    "task_scheduler/task_traits_unittest.cc",
     "task_scheduler/task_unittest.cc",
     "task_scheduler/test_task_factory.cc",
     "task_scheduler/test_task_factory.h",
     "task_scheduler/test_utils.cc",
     "task_scheduler/test_utils.h",
     "template_util_unittest.cc",
     "test/histogram_tester_unittest.cc",
     "test/mock_callback_unittest.cc",
     "test/scoped_mock_time_message_loop_task_runner_unittest.cc",
     "test/scoped_task_scheduler_unittest.cc",
@@ skipping 259 matching lines @@
 
 if (enable_nocompile_tests) {
   nocompile_test("base_nocompile_tests") {
     sources = [
       "bind_unittest.nc",
       "callback_list_unittest.nc",
       "callback_unittest.nc",
       "memory/ref_counted_unittest.nc",
       "memory/weak_ptr_unittest.nc",
       "metrics/histogram_unittest.nc",
+      "task_scheduler/task_traits_unittest.nc",
     ]
 
     deps = [
       ":base",
       "//base/test:run_all_unittests",
       "//testing/gtest",
     ]
   }
 }
 
@@ skipping 287 matching lines @@
 }
 
 fuzzer_test("base_json_correctness_fuzzer") {
   sources = [
     "json/correctness_fuzzer.cc",
   ]
   deps = [
     ":base",
   ]
 }