RFR: JDK-8297309: Memory leak in ShenandoahFullGC

[Justin King]

Signed-off-by: Justin King <jcking at google.com>

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Commit messages:
 - Fix memory leak in ShenandoahFullGC

Changes: https://git.openjdk.org/jdk/pull/11255/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11255&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297309
  Stats: 5 lines in 2 files changed: 5 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/11255.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11255/head:pull/11255

PR: https://git.openjdk.org/jdk/pull/11255