RFR: 8298175: JFR: Common timestamp for periodic events

[Erik Gahlin]

Could I have review of infrastructure that makes it easier to write periodic events with the same timestamp.

Testing: jdk/jdk/jfr + tier1 + tier2

Thanks
Erik

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Commit messages:
 - Fixes
 - Fixes
 - Initial

Changes: https://git.openjdk.org/jdk/pull/11541/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11541&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8298175
  Stats: 24 lines in 5 files changed: 12 ins; 0 del; 12 mod
  Patch: https://git.openjdk.org/jdk/pull/11541.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11541/head:pull/11541

PR: https://git.openjdk.org/jdk/pull/11541