RFR(S): JDK-8040002: Clean up code and code duplication in re-diryting cards for verification

[Thomas Schatzl]

Hi all,

  can I have reviews for the following short cleanup? While implementing
8019342 I found that there is some opportunity to clean up code in the
various card closures in G1.

There is some code duplication, and the verification card closure code
still assumes the presence of a perm gen. There are also some hardcoded
card table values for clean/dirty cards.

CR:
https://bugs.openjdk.java.net/browse/JDK-8040002

Webrev:
http://cr.openjdk.java.net/~tschatzl/8040002/webrev/

Testing:
jprt

Thanks,
  Thomas