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

[BuddyLiao]

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

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Commit messages:
 - 8272611: Use parallel heap inspection when print classhisto info in gc log
 - Merge branch 'openjdk:master' into master
 - 8266193: BasicJMapTest does not include testHistoParallel methods

Changes: https://git.openjdk.java.net/jdk/pull/5156/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5156&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8272611
  Stats: 2 lines in 1 file changed: 1 ins; 0 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