RFR: 8217858: ZGC: Clean up ZDriver

[Erik Österlund]

+1

On 2019-01-28 10:01, Per Liden wrote:
> Various structural and naming cleanups in ZDriver. Most notably, the 
> ZOperationClosure types were replaced by true VM operation types.
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8217858
> Webrev: http://cr.openjdk.java.net/~pliden/8217858/webrev.0
> 
> /Per