RFR (S): 8232776: G1 should always take rs_length_diff into account when predicting rs_lengths

[Thomas Schatzl]

Hi all,

   can I have reviews for this small change that makes G1 always use the 
error term for rs-length prediction, not only if G1 sees fit.

While rs length prediction is still kind of bad even with this change 
(and seemingly a band-aid), with that change it is a bit better. While 
there is a "real" fix for RS length estimation coming that so far looks 
really good, this change decreases complexity of further changes in 
G1Policy enough while improving the estimation.

CR:
https://bugs.openjdk.java.net/browse/JDK-8232776
Webrev:
http://cr.openjdk.java.net/~tschatzl/8232776/webrev/
Testing:
hs-tier1-5

Thanks,
   Thomas