RFR: 8237364: Add early validation to the jdk.jfr.Recording constructor

[Erik Gahlin]

Hi,

Could I have a review of a fix that adds validation to the Recording 
constructor.

Bug:
https://bugs.openjdk.java.net/browse/JDK-8237364

Webrev:
http://cr.openjdk.java.net/~egahlin/8237364/

Testing:
jdk/jdk/jfr

Thanks
Erik