RFR: 8278109: gc/metaspace/TestPerfCountersAndMemoryPools.java fails with Used out of sync: expected 1028976 to equal 1029224

[Leonid Mesnik]

The test is updated to don't fail if 'MemoryPoolMXBean::getUsage().getUsed()' allocate new classes intermittently.

The problem was reproduced in repo-loom only. However it makes sense to push this fix into jdk/jdk separately to reduce overall push and increase test stability.

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Commit messages:
 - 8278109: gc/metaspace/TestPerfCountersAndMemoryPools.java fails with Used out of sync: expected 1028976 to equal 1029224

Changes: https://git.openjdk.java.net/jdk/pull/8408/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8408&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8278109
  Stats: 16 lines in 1 file changed: 9 ins; 0 del; 7 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8408.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8408/head:pull/8408

PR: https://git.openjdk.java.net/jdk/pull/8408