RFR: 8309296: jdk/jfr/event/runtime/TestAgentEvent.java fails due to "missing" dynamic JavaAgent

[Erik Gahlin]

Could I have a review of a test fix.

Problem is that events use another clock source than Recording::getStartTime(). 

I added -XX:+UnlockExperimentalVMOptions -XX:-UseFastUnorderedTimeStamps in case the Attach thread and the Main thread executes on different cores and there could be drift. The flags may, or may not, also fix the time source issue. Regardless, I think it's prudent to do time comparison against an event, not the recording timestamps, because they are different things conceptually and there are tweaks to the recording timestamps (to make them work well with Instant.now(), not the event clock source)

Testing: jdk/jdk/jfr/event/runtime/TestAgentEvent.java

Thanks
Erik

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Commit messages:
 - Initial

Changes: https://git.openjdk.org/jdk/pull/14572/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14572&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8309296
  Stats: 38 lines in 1 file changed: 21 ins; 0 del; 17 mod
  Patch: https://git.openjdk.org/jdk/pull/14572.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14572/head:pull/14572

PR: https://git.openjdk.org/jdk/pull/14572