Request for review JDK-8065402, , G1 does not expand marking stack when mark stack overflow happens during concurrent marking

[Kim Barrett]

> On Apr 27, 2017, at 4:39 PM, Alexander Harlap <alexander.harlap at oracle.com> wrote:
> I like this idea - to eliminate should_expand tracking. It really straightens mark stack expansion mechanism.
>> 
> Revised change is here: http://cr.openjdk.java.net/~aharlap/8065402/webrev.01/
> I retested change.

Looks good.