RFR: 8269294: Verify_before/after_young_collection should execute all verification [v3]

[Thomas Schatzl]

> Hi all,
> 
>   can I have reviews for this tiny change that moves all verification from `do_collection_pause_at_safepoint_helper()` to `verify_before/after_young_collection`?
> 
> I actually removed one call to `_hrm.verify_optional()` because it is already called in `_verifier->verify_region_sets_optional` although they are not completely equivalent as one call is `DEBUG_ONLY` and the other `NOT_PRODUCT`, but nobody is probably using the optimized build anyway. I can re-add the missing call if required.
> 
> Testing: tier1
> 
> Thanks,
>   Thomas
> 
> P.S: this is based on PR#4539, so it would be nice if it could be reviewed before this.

Thomas Schatzl has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains three commits:

 - Merge branch 'master' of https://git.openjdk.java.net/jdk into submit/8269294-merge-verify-stages
 - Fix young gc verify stages
 - Initial implementation

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

Changes: https://git.openjdk.java.net/jdk/pull/4586/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4586&range=02
  Stats: 9 lines in 1 file changed: 3 ins; 6 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4586.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4586/head:pull/4586

PR: https://git.openjdk.java.net/jdk/pull/4586