RFR: 8246436: JFR: Avoid parsing metadata.xml during startup

[Erik Gahlin]

Hi,

Could I have review of an enhancement that will avoid parsing the XML metadata for the JVM events during startup/runtime.

Thanks to Magnus for helping out with changes to the make files. 

Bug:
https://bugs.openjdk.java.net/browse/JDK-8246436

Webrev:
http://cr.openjdk.java.net/~egahlin/8246436/

Testing: tier1+tier2 + jdk/jdk/jfr

Thanks
Erik