RFR (XS): CR 6908215: SEGV with G1PolicyVerbose=2 debug flag

[John Cuthbertson]

Hi Everyone,

Can I have a couple of volunteers to review the changes for this CR - 
the changes can be found at 
http://cr.openjdk.java.net/~johnc/6908215/webrev.0/

During testing of the fix for 6902115 - I turned this flag to enable 
some heap-region based tracing. The test case SEGV'd after a clean up 
pause. The code needs to handle the case when there is a NULL entry in 
the growable array that is being walked and printed (c.f. the code in 
CollectionSetChooser::verify).

Testing: the 6902115 test case with G1PolicyVerbose=0,1,2

Thanks,

JohnC