RFR(M): 7004681: G1: Extend marking verification to marking phase of Full GCs

[John Cuthbertson]

Hi Everyone,

A new webrev for this CR can be found at: 
http://cr.openjdk.java.net/~johnc/MarkSweep-VerifyMark/webrev.3.

I'd like to get at least another person look over these changes (Tony 
has already looked at an earlier version). The latest webrev includes 
skipping the region set verification if the verification was called from 
a full GC (in G1 the region sets are torn down at the start of the full 
GC and so the verification will give a false failure).

Testing: GC test suite with +VerifyDuringGC with and without G1.

Thanks,

JohnC