[jdk15u-dev] RFR: 8257999: Parallel GC crash in gc/parallel/TestDynShrinkHeap.java: new region is not in covered_region

[Olga Mikhaltsova]

I'd like to backport JDK-8257999 to jdk15u for parity with jdk11u.
The original patch applied manually due to the slight context changes.
All regular tests passed.

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Commit messages:
 - Backport 61390d8e452058efe00ca8ce833baa879fbb9c9e

Changes: https://git.openjdk.java.net/jdk15u-dev/pull/99/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk15u-dev&pr=99&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8257999
  Stats: 4 lines in 1 file changed: 3 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk15u-dev/pull/99.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk15u-dev pull/99/head:pull/99

PR: https://git.openjdk.java.net/jdk15u-dev/pull/99