RFR: 8281297: TestStressG1Humongous fails with guarantee(is_range_uncommitted)

[Leo Korinth]

TestStressG1Humongous passes 200 times with this change. I have started a new windows run with 1000 iterations. Without the fix the testcase will usually fail a few times when iterating 100 times. I have also started a tier 1-3 run.

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Commit messages:
 - 8281297: TestStressG1Humongous fails with guarantee(is_range_uncommitted)

Changes: https://git.openjdk.java.net/jdk/pull/8560/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8560&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8281297
  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8560.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8560/head:pull/8560

PR: https://git.openjdk.java.net/jdk/pull/8560