RFR: 8288982: JFR: Log event streaming actions

[Erik Gahlin]

Could I have a review of a change that log event actions for an EventStream. Purpose is to find cause of intermittent failure of TestOnEvent. See https://bugs.openjdk.org/browse/JDK-8255404

Testing:  test/jdk/jdk/jfr

Thanks
Erik

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Commit messages:
 - Fix formatting
 - Initial

Changes: https://git.openjdk.org/jdk/pull/9244/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9244&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8288982
  Stats: 17 lines in 3 files changed: 16 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/9244.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9244/head:pull/9244

PR: https://git.openjdk.org/jdk/pull/9244