RFR: 8256830: misc tests failed with "assert(env->is_enabled(JVMTI_EVENT_OBJECT_FREE)) failed: checking"

[Coleen Phillimore]

The ServiceThread cleaning used a stale ObjectFree state when calling remove_dead_entries, because another thread had concurrently set is_enabled to false.  Add a lock around setting/resetting the lock event state and retest the state under a lock.  Ran the test 100s of time without failure, where otherwise it fails very quickly.
Tested with tier2,3 and running tiers 4,5,6 in progress.
Thanks to Kim for his previous feedback.

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Commit messages:
 - 8256830: misc tests failed with "assert(env->is_enabled(JVMTI_EVENT_OBJECT_FREE)) failed: checking"

Changes: https://git.openjdk.java.net/jdk/pull/1439/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1439&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8256830
  Stats: 25 lines in 3 files changed: 23 ins; 1 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1439.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1439/head:pull/1439

PR: https://git.openjdk.java.net/jdk/pull/1439