RFR: 8254565: JFR: Incorrect verification of mirror events

[Erik Gahlin]

Hi,

Could I have a review of a fix that improves the verification of mirror events. 

Mirror events is an internal mechanism used by JDK events that can't depend on the jdk.jfr module, today only events defined in java.base. The verification is a sanity check to make sure the field layout of the event and the mirror does not differ. The verification now verifies field type and it handles the unlikely case somebody adds a field to java.lang.Object (for experimentation) by always walking the whole class hierarchy of the mirror. 

Testing: jdk/jdk/jfr

Thanks
Erik

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Commit messages:
 - Initial

Changes: https://git.openjdk.java.net/jdk/pull/3600/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3600&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8254565
  Stats: 25 lines in 1 file changed: 10 ins; 9 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3600.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3600/head:pull/3600

PR: https://git.openjdk.java.net/jdk/pull/3600