[jdk11u-dev] RFR: 8266352: Add parallel heap iteration for jmap –histo [v2]

[BuddyLiao]

> 8215624: Add parallel heap iteration for jmap -histo
> 8251570: JDK-8215624 causes assert(worker_id <' _n_workers) failed: Invalid worker_id
> 8253763: ParallelObjectIterator should have virtual destructor

BuddyLiao has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR.

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Changes:
  - all: https://git.openjdk.java.net/jdk11u-dev/pull/75/files
  - new: https://git.openjdk.java.net/jdk11u-dev/pull/75/files/3bcb48cb..52cbf2f6

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=75&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=75&range=00-01

  Stats: 290 lines in 14 files changed: 6 ins; 250 del; 34 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/75.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/75/head:pull/75

PR: https://git.openjdk.java.net/jdk11u-dev/pull/75