RFR: 8152711: Create a non-template Log wrapper class

[Stefan Karlsson]

Hi all,

Please review this patch to introduce type-erased Log and LogTarget 
wrapper classes. These classes can be used where we don't want or can't 
use the template parameters associated with the Log and LogTarget classes.

http://cr.openjdk.java.net/~stefank/8152711/webrev.01
https://bugs.openjdk.java.net/browse/JDK-8152711

The patch is applied on top of the patch in:
http://mail.openjdk.java.net/pipermail/hotspot-dev/2016-March/022304.html

I've received internal feedback that we probably want to reuse the 
LogTagSet instances. I'd prefer if that could be prototyped and 
implemented as a separate RFE.

I've changed the implementation of GCTraceTime to show how LogHandles 
can be used to lower the amount of template parameters used throughout 
the implementation.

Test: new internal vm test, jprt

Thanks,
StefanK