RFR(S): 7016955: G1: remove the is_zeroed parameter from the HeapRegion constructor

[John Cuthbertson]

Hi Everyone,

Can I have a volunteer to review the changes, which were contributed by 
Brandon Mitchell at Twitter, for this CR? The webrev can be found at: 
http://cr.openjdk.java.net/~johnc/7016955/webrev.0/

Summary:
When Tony removed the zero filling thread, the is_zeroed parameter in 
the HeapRegion constructor became unused. These changes remove that 
unused parameter and clean up the HeapRegion initialization code.

Testing:
SPECjvm98 and SPECjbb2005 on Linux (Brandon); GC test suite on solaris 
(x86 and sparc) and jprt (JohnC)

Thanks,

JohnC