RFR: 8027675: Full collections with Serial slower in JDK 8 compared to 7u40

[Stefan Johansson]

Hi all,

Can I have a couple reviews for this fix for:
https://bugs.openjdk.java.net/browse/JDK-8027675

Webrev:
http://cr.openjdk.java.net/~sjohanss/8027675/webrev.00/

Summary:
When doing permgen removal we had to change the way classes were marked 
and handled in the GC. When doing this we ended up doing some things a 
little less efficient than before. The regression is easy to reproduce 
and when doing a JFR recording we can see that we now spend more time in 
both the mark and adjust phase.

To improve the mark phase:
* Enabled the calls to follow_klass to be inlined.
* Reduce the extensive amount of calls to follow_class_loader in 
follow_klass and instead just mark the klass holder (the class loader or 
the java mirror) for the given klass.

To improve the adjust phase:
* All calls to adjust_klass have been removed since this is already 
handled by processing the ClassLoaderDataGraph.

Testing:
* Manually ran SPECjbb2005 to verify fixing the regression
* JPRT for functional sanity testing
* Nashorn tests to stress anonymous classes

Thanks,
StefanJ