JDK 9 RFR for 8036841 : Reuse no-perms AccessControlContext object when performing isAuthorized check

[Sean Mullan]

This is a fix to avoid creating multiple no-perms ACC objects for access 
control checks. Since this is required in an uncommon scenario, I used 
the Initialization on demand holder pattern to only create it under 
those circumstances.

webrev: http://cr.openjdk.java.net/~mullan/webrevs/8036841/webrev.01/

--Sean