RFR: 8373262: Parallel: gc/metaspace/CompressedClassSpaceSizeInJmapHeap.java fails

[Albert Mingkun Yang]

[JDK-8367541](https://bugs.openjdk.org/browse/JDK-8367541) changes the fields in `src/hotspot/share/gc/parallel/parallelScavengeHeap.hpp` to be non-static. The corresponding access in `src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/gc/parallel/ParallelScavengeHeap.java` should be updated as well.

`TEST=gc/metaspace/CompressedClassSpaceSizeInJmapHeap.java JTREG_JAVA_OPTIONS=-XX:+UseParallelGC` fails consistently without the fix and passes with the fix.

Test: tier1-2

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

Commit messages:
 - src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/gc/parallel/ParallelScavengeHeap.java

Changes: https://git.openjdk.org/jdk/pull/28700/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28700&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8373262
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/28700.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28700/head:pull/28700

PR: https://git.openjdk.org/jdk/pull/28700