This is mainly a note to myself to save me from looking up the details very time I need it. I can just go to my own post.
To use Autotrace in SQL you need to grant the schema the PLUSTRACE role.
But in SQL Developer you need the PLUSTRACE role that has a few additional privileges.
Connect to SYS as sysdba and run the following.
grant select on v_$session to plustrace; grant select on v_$sql_plan to plustrace; grant select on v_$sql_plan_statistics to plustrace; grant select on v_$sql to plustrace;
Now you will be able to run Autotrace in SQL Developer.
(Make sure to reconnect your SQL Developer connection so that the privileges can be picked up).