RFR: 8201826: G1: Don't invoke WeakProcessor if mark stack has overflowed

[Thomas Schatzl]

Hi Kim,

On Thu, 2018-04-19 at 00:56 -0400, Kim Barrett wrote:
> Please review this change to G1 concurrent marking to not invoke the
> WeakProcessor when the mark stack has overflowed, as the is-alive
> closure is not accurate in that situation.
> 
> CR:
> https://bugs.openjdk.java.net/browse/JDK-8201826
> 
> Webrev:
> http://cr.openjdk.java.net/~kbarrett/8201826/open.00/
> 
> Testing:
> {jdk,hs}-tier{1,2,3} on all Oracle supported platforms.
> 

  looks good.

Thomas