RFR [8u40] 8048268, 8057722 Code root migration

[Mikael Gerdin]

Hi all,

I'd like to backport 8048268 and the related bugfix 8057722 to 8u40 to reduce 
the performance impact of code root migration.

The original patch for 8048268 did not apply cleanly due to some spelling and 
style changes.

These changes depend on 8056084 which is out for review on hotspot-dev.
I plan to push these changes together once they're through review.

Review threads: 
http://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2014-August/010582.html
http://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2014-September/010709.html

Bugs:
https://bugs.openjdk.java.net/browse/JDK-8048268
https://bugs.openjdk.java.net/browse/JDK-8057722

Webrevs:
http://cr.openjdk.java.net/~mgerdin/8048268/8u/webrev/
http://cr.openjdk.java.net/~mgerdin/8057722/8u/webrev/

/Mikael