RFR: 8274338: com/sun/jdi/RedefineCrossEvent.java failed "assert(m != __null) failed: NULL mirror"

[Coleen Phillimore]

The MultiArray_lock isn't held when restoring shared arrays, so an observer can find one that isn't completely restored.
Tested with tier1-3 in progress, and CDS tests locally.  Not really reproduceable otherwise even with sleeps.

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Commit messages:
 - 8274338: com/sun/jdi/RedefineCrossEvent.java failed "assert(m != __null) failed: NULL mirror"

Changes: https://git.openjdk.java.net/jdk/pull/5935/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5935&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8274338
  Stats: 3 lines in 1 file changed: 3 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5935.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5935/head:pull/5935

PR: https://git.openjdk.java.net/jdk/pull/5935