RFR: 8315149: Add hsperf counters for CPU time of internal GC threads [v3]

[Jonathan Joo]

> 8315149: Add hsperf counters for CPU time of internal GC threads

Jonathan Joo has updated the pull request incrementally with one additional commit since the last revision:

  address remainder of dholmes' comments

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/15082/files
  - new: https://git.openjdk.org/jdk/pull/15082/files/557dbfa6..eb911ee1

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15082&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15082&range=01-02

  Stats: 19 lines in 7 files changed: 8 ins; 7 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/15082.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15082/head:pull/15082

PR: https://git.openjdk.org/jdk/pull/15082