Request for review - 7197557

[Jon Masamitsu]

NPG: nsk/sysdict/vm/stress/chain/chain004 hangs intermittently

The code that was doing a GC to find dead class loaders so that metadata
could be freed does not correctly account for GC_locker activity (i.e., use
of JNI critical sections which stall GC).  Added code to recognize if
a GC_locker is active and expand the Metaspace and allocate out of the
expanded area.  If the expansion cannot provide metadata, wait for
the GC_locker to inactivate so that a GC can be done.

http://cr.openjdk.java.net/~jmasa/7197557/webrev.00/

Note that there are three places in the different GC's that need to
account for GC_locker activity.  I am investigating whether this
code can be unified.