RFR: 8272611: Use parallel heap inspection when print classhisto info in gc log [v2]

[BuddyLiao]

> 8272611: Use parallel heap inspection when print classhisto info in gc log

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/jdk/pull/5156/files
  - new: https://git.openjdk.java.net/jdk/pull/5156/files/a896a21b..ec63957f

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5156&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5156&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 1 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5156.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5156/head:pull/5156

PR: https://git.openjdk.java.net/jdk/pull/5156