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

[BuddyLiao]

I have built it on linux x86_64 and run test-tier1

---------
### Progress
- [x] Change must not contain extraneous whitespace
- [x] Commit message must refer to an issue
- [ ] Change must be properly reviewed



### Reviewing
<details><summary>Using <code>git</code></summary>

Checkout this PR locally: \
`$ git fetch https://git.openjdk.java.net/jdk pull/5158/head:pull/5158` \
`$ git checkout pull/5158`

Update a local copy of the PR: \
`$ git checkout pull/5158` \
`$ git pull https://git.openjdk.java.net/jdk pull/5158/head`

</details>
<details><summary>Using Skara CLI tools</summary>

Checkout this PR locally: \
`$ git pr checkout 5158`

View PR using the GUI difftool: \
`$ git pr show -t 5158`

</details>
<details><summary>Using diff file</summary>

Download this PR as a diff file: \
<a href="https://git.openjdk.java.net/jdk/pull/5158.diff">https://git.openjdk.java.net/jdk/pull/5158.diff</a>

</details>

-------------

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

Changes: https://git.openjdk.java.net/jdk/pull/5158/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5158&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/5158.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5158/head:pull/5158

PR: https://git.openjdk.java.net/jdk/pull/5158