Review request: 8025996: Track metaspace usage when metaspace is expanded

[Stefan Karlsson]

http://cr.openjdk.java.net/~stefank/8025996/webrev.00

Previously, the Metaspace memory usage was only tracked at the end of 
the GCs. This causes the MemoryPoolMXBean.getUsageThreshold(…) 
functionality to fail for the Metaspace memory pools. This patch adds 
tracking of Metaspace usage when a new Metachunk is fetched.

This patch builds upon the patch in:
http://mail.openjdk.java.net/pipermail/hotspot-dev/2013-October/011166.html
Review request: 8024547: MaxMetaspaceSize should limit the committed 
memory used by the metaspaces

This patch has been tested with the fix for:
https://bugs.openjdk.java.net/browse/JDK-7196801
NPG: Fix java/lang/management/MemoryMXBean/LowMemoryTest2

The fix for 7196801 will be done in a separate review request since the 
test is located in jdk repository and the fix for 8025996 is done in the 
hotspot repository.

thanks,
StefanK