CRR (XS): 7125281: G1: heap expansion code is replicated

[Tony Printezis]

Hi all,

I'd like one code review for this very small change (I already have one 
from Bengt, thanks!):

http://cr.openjdk.java.net/~tonyp/7125281/webrev.0/

We had accidentally replicated the code that expands the heap.

Tony