RFR: 8292265: Add old gen used field at G1HeapSummary JFR event.

[Sangheon Kim]

Hi all,

Can I have reviews for this change which adds 'old gen used' field at existing G1HeapSummary event?

Testing: tier1 ~ tier3

Thanks,
Sangheon

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Commit messages:
 - 8292265: Add old gen used field at G1HeapSummary JFR event

Changes: https://git.openjdk.org/jdk/pull/11303/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11303&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8292265
  Stats: 10 lines in 4 files changed: 6 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/11303.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11303/head:pull/11303

PR: https://git.openjdk.org/jdk/pull/11303