RFR: 8229017: ZGC: Various cleanups of ZVerify

[Per Liden]

Stefan asked me to break out the ZStatTimerDisable fix into a separate 
fix, which I did (JDK-8229135), so here's an updated webrev without that 
part:

http://cr.openjdk.java.net/~pliden/8229017/webrev.1

/Per

On 8/2/19 11:40 AM, Per Liden wrote:
> Hi,
> 
> This patch does various cleanups of ZVerify, basically a post-commit 
> review of JDK-8227175. The patch mostly moves some code around and 
> adjusts a few names. However, there's also one bug fix and one logic 
> change:
> 
> * ZVerify::roots_strong() didn't have a ZStatTimerDisable.
> 
> * The call to ClassLoaderDataGraph::clear_claimed_marks() was moved from 
> ZMarkConcurrentRootsTask() to ZConcurrentRootsIterator(), and now only 
> clears the claim type the iterator actually used (instead of all types).
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8229017
> Webrev: http://cr.openjdk.java.net/~pliden/8229017/webrev.0
> 
> /Per