TaskScheduler: Make Task::traits const.

base/task_scheduler/task.h

Index: base/task_scheduler/task.h
diff --git a/base/task_scheduler/task.h b/base/task_scheduler/task.h
index ee9f7a4c23636e84c3508e96725f28a62c90b117..b2fa7661b569686767e013af7c6c1d23559d283e 100644
--- a/base/task_scheduler/task.h
+++ b/base/task_scheduler/task.h
@@ -29,12 +29,12 @@ struct BASE_EXPORT Task : public PendingTask {
   // automatically adjusted to SKIP_ON_SHUTDOWN.
   Task(const tracked_objects::Location& posted_from,
        const Closure& task,
-       const TaskTraits& traits_in,
+       const TaskTraits& traits,
        const TimeDelta& delay);
   ~Task();
 
   // The TaskTraits of this task.
-  TaskTraits traits;
+  const TaskTraits traits;
 
   // The time at which the task was inserted in its sequence. For an undelayed
   // task, this happens at post time. For a delayed task, this happens some